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Background: Olaparib (O) is approved for the treatment of HER2[-] patients (pts) with early or metastatic breast cancer and a germline BRCA mutation. Nevertheless, there is no evidence that HER2[+] tumors are resistant to PARPi. Preclinical data support that HER2[+] cells are sensitive to PARPi and strongly suggest that PARP inhibition augments the efficacy of trastuzumab (T). To test whether PARPi is synergistic with anti-HER2 therapy, the OPHELIA study has assessed the efficacy and safety of O in combination with T in pts with HER2[+] germinal BRCA-mutated advanced breast cancer (ABC). Methods: OPHELIA (NCT03931551) is an open-label, multicenter, single-arm, phase II trial. The study enrolled pts aged ≥18 years diagnosed of HER2[+] ABC with germinal deleterious mutations in BRCA1 or BRCA2 who had received at least one prior systemic regimen for advanced disease (including a pertuzumab- or trastuzumab emtansine based regimen). Pts received O (300 mg oral, twice daily) plus T (either loading dose of 8 mg/kg IV infusion, and subsequent 3-weekly doses of 6 mg/kg IV infusion; or 600 mg SC injection, on day 1 of every 21-day cycle) until disease progression, unacceptable toxicity, or consent withdrawal. Primary endpoint was investigator-assessed clinical benefit rate (CBR) for at least 24 weeks as per RECIST v.1.1. Secondary endpoints included overall response rate (ORR), duration of response (DoR), progression-free survival (PFS), overall survival (OS); and safety and tolerability as per NCI-CTCAE v.5.0. The primary analysis evaluated CBR (H0: ≤5%; H1: ≥30%) based on exact binomial test. Sample size was designed to attain a 90% power at 10% one-sided alpha level. Results: From Mar 25, 2019, through Mar 2, 2022, 5 pts (from a total of 42 pts evaluated) were enrolled at 17 sites in Spain. Median age was 37.0 (range 32–54) years, 1 (20.0%) patient was male, 4 (80.0%) pts carried germinal BRCA2 mutations, 4 (80.0%) pts had received ≥ 3 advanced disease treatments lines, and 4 (80.0%) pts presented ≥ 2 metastatic sites. At data cutoff (Mar 2, 2022), with a median follow-up of 18.7 months (min: 11.7; max: 22.1), 40.0% of pts remained on therapy. CBR at 24 weeks was 80.0% meeting the primary endpoint (4 of 5 pts; 95% CI, 28.4% to 99.5%, p< 0.001). ORR (1 complete and 2 partial responses) was 60.0% (95% CI, 17.4% to 94.7%), and median DoR was 3.8 months (95% CI, 2.5 to 8.3 months). Two (40.0%) pts had PFS events due to disease progression at 5.2 and 1.2 months, respectively. Rest of pts were treated for 5.5, 11.2, and 19.0 months. There were 2 (40.0%) deaths at 14.0 and 18.5 months. The most common non-hematological treatment emergent adverse events (TEAEs) of any grade (G) were fatigue (60.0%; 0% G≥3), nausea (60.0%; 0% G≥3), vomiting (40.0%; 0% G≥3), and back pain (40.0%; 0% G≥3). Anemia (40.0%; 20.0% G≥3) and lymphopenia (40.0%; 20.0% G≥3) were the most frequent hematological TEAEs. One (20.0%) patient discontinued treatment because of a drug-related TEAE (leukopenia). A dose reduction of O was reported in 1 (20.0%) patient. No treatment-related deaths were reported. Conclusions: HER2 overexpression in germline BRCA-mutated ABC is infrequent. The activity observed in these 5 pts indicates that O+T combination might be of help in this group of pts. We strongly believe that randomized data are not needed, and RWE studies might help us to understand the real activity of this combination. Toxicity was as expected. Citation Format: José E. Alés-Martínez, Judith Balmaña, Pedro Sánchez-Rovira, Francisco Javier Salvador Bofill, José Ángel García-Sáenz, Isabel Pimentel, Serafin Morales Murillo, Adela Fernández, Ainhara Lahuerta Martínez, Neus Ferrer, Pilar Zamora, Begoña Bermejo, Tamara Díaz-Redondo, María Helena Lopez-Ceballos, María Galán, Andrea Malfettone, Laura Calabuig, Miguel Sampayo-Cordero, José Manuel Pérez-García, Javier Cortés, Antonio Llombart-Cussac. Olaparib plus Trastuzumab in HER2[+] BRCA-Mutated Advanced Breast Cancer Patients: The OPHELIA Study [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-07-29.

Background: Breast cancer with low HER2 expression (HER2-low) is of high clinical relevance because of new therapeutic options with antibody-drug conjugates. We have recently shown in a large cohort from neoadjuvant clinical trials that HER2-low breast cancer has different molecular characteristics as well as different clinical outcomes compared to HER2-zero. Considering the positive correlation between HER2-low expression and hormone receptor positivity observed consistently in many investigations, we have extended our analysis to HR+ tumors from the post-neoadjuvant PenelopeB trial. In PenelopeB, patients with HR+ breast cancer and residual disease after neoadjuvant chemotherapy (NACT) were randomized to post-neoadjuvant palbociclib versus placebo in addition to endocrine therapy. We evaluated the molecular phenotype and clinical outcomes of HER2-low compared to HER2-zero patients. Methods: A total of 1250 patients were randomized, HER2 status was available for 1151 tumors from pretherapeutic core biopsy, determined mainly by local pathology, and from 1213 tumors from the post-NACT sample, determined as part of central pathology. For 1119 patients a paired HER2-status was both available. HER2-zero was defined as IHC0 and HER2-low-positive was defined as IHC1+ or IHC2+/ISH-. Gene expression analysis of 2549 genes using the HTG oncology biomarker panel was performed in 620 pretherapeutic biopsies and 780 post-NACT residual tumor samples, with 539 paired gene expression samples. Breast cancer subtypes were determined using the AIMS approach. Results: In pretherapeutic biopsies, 695 tumors (60%) were HER2-low and 457 (40%) were HER2-zero. A HER2-low status in the biopsy was significantly linked to improved iDFS (HR 0.76 (0.60-0.96; p=0.02). In residual tumors, 632 tumors (60%) were HER2-low and 581 (40%) were HER2-zero, without any prognostic impact of HER2 low status. In addition, a shift of HER2-low-status comparing core biopsy and residual tumor was observed in 415 (37%) of 1119 tumors. 161 (14%) had a shift from HER2-zero to HER2-low and 254 (23%) shifted from HER2-low to HER2-zero. A shift from HER2-zero to HER2-low in the post-NACT samples was significantly linked to reduced iDFS (HR 1.43 [95%CI 1.01-2.01]), p=0.04), compared to HER2-low group, while a shift from HER2-low to HER2-zero was associated with better iDFS compared to HER2-zero group, although not statistically significant (p=0.17). We did not observe a significant correlation of HER2-low status and AIMS molecular subtypes. In particular, the HER2-enriched (HER2E) subtype was assigned to only 4.3% of HER2-zero and 3.1% of HER2-low tumors. Significant iDFS differences were observed for HER2-low-status in combination with AIMS subtypes (lumB/basal/HER2E vs. lumA/normL; overall p-value < 0.0001) for both pretherapeutic biopsies and residual tumor. Patients with post-NACT HER2-low tumors had an improved survival in the subgroups of aggressive AIMS subtypes (lumB/basal/HER2E), but not in the less aggressive AIMs subtypes (lumA/normL), with a positive test for interaction (p=0.02). For the pre-NACT samples a similar, but non-significant trend was observed. We evaluated a total of 620 core biopsies for differences in gene expression comparing HER2-low and HER2-zero tumors. A total of 417 genes were statistically significantly different, but in a hierarchical clustering there was no clear separation of HER2-low and HER2-zero tumors. Conclusions: In the PenelopeB cohort of HR+ tumors, a HER2-low status in pretherapeutic core biopsies is related to improved disease-free survival, especially for those tumors that have a more aggressive intrinsic subtype. A shift of HER2-low status was observed before and after chemotherapy, indicating an adaptation of the pathway activity to therapy-induced stress, which might become relevant for future diagnostic and therapeutic approaches. Citation Format: Carsten Denkert, Miguel Martín, Michael Untch, Hervé R. Bonnefoi, Erik S. Knudsen, Seock-Ah Im, Angela DeMichele, Agnieszka Witkiewicz, Laura Van ’t Veer, Sung-Bae Kim, Harry D. Bear, Nicole McCarthy, Karen Gelmon, Frederik Marmé, José Ángel García-Sáenz, Nicholas Turner, Federico Rojo, Martin Filipits, Lesley-Ann Martin, Peter A. Fasching, Christian Schem, Catherine M. Kelly, Toralf Reimer, Masakazu Toi, Hope Rugo, Michael Gnant, Andreas Makris, Yuan Liu, Karsten Weber, Sivaramakrishna Rachakonda, Sibylle Loibl. HER2-06 Outcome analysis of HER2-zero or HER2-low hormone receptor-positive (HR+) breast cancer patients - characterization of the molecular phenotype in combination with molecular subtyping [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr HER2-06.

Adjuvant therapy; Breast cancer; Olaparib Terapia adyuvante; Cáncer de mama; Olaparib Teràpia adjuvant; Càncer de mama; Olaparib Background The randomized, double-blind OlympiA trial compared 1 year of the oral poly(adenosine diphosphate-ribose) polymerase inhibitor, olaparib, to matching placebo as adjuvant therapy for patients with pathogenic or likely pathogenic variants in germline BRCA1 or BRCA2 (gBRCA1/2pv) and high-risk, human epidermal growth factor receptor 2-negative, early breast cancer (EBC). The first pre-specified interim analysis (IA) previously demonstrated statistically significant improvement in invasive disease-free survival (IDFS) and distant disease-free survival (DDFS). The olaparib group had fewer deaths than the placebo group, but the difference did not reach statistical significance for overall survival (OS). We now report the pre-specified second IA of OS with updates of IDFS, DDFS, and safety. Patients and methods One thousand eight hundred and thirty-six patients were randomly assigned to olaparib or placebo following (neo)adjuvant chemotherapy, surgery, and radiation therapy if indicated. Endocrine therapy was given concurrently with study medication for hormone receptor-positive cancers. Statistical significance for OS at this IA required P < 0.015. Results With a median follow-up of 3.5 years, the second IA of OS demonstrated significant improvement in the olaparib group relative to the placebo group [hazard ratio 0.68; 98.5% confidence interval (CI) 0.47-0.97; P = 0.009]. Four-year OS was 89.8% in the olaparib group and 86.4% in the placebo group (Δ 3.4%, 95% CI −0.1% to 6.8%). Four-year IDFS for the olaparib group versus placebo group was 82.7% versus 75.4% (Δ 7.3%, 95% CI 3.0% to 11.5%) and 4-year DDFS was 86.5% versus 79.1% (Δ 7.4%, 95% CI 3.6% to 11.3%), respectively. Subset analyses for OS, IDFS, and DDFS demonstrated benefit across major subgroups. No new safety signals were identified including no new cases of acute myeloid leukemia or myelodysplastic syndrome. Conclusion With 3.5 years of median follow-up, OlympiA demonstrates statistically significant improvement in OS with adjuvant olaparib compared with placebo for gBRCA1/2pv-associated EBC and maintained improvements in the previously reported, statistically significant endpoints of IDFS and DDFS with no new safety signals. Funding for this work, which was conducted as a collaborative partnership among the Breast International Group, NRG Oncology, Frontier Science, AstraZeneca, and Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, U.S.A. (MSD), was provided by the National Institutes of Health (grant numbers: U10CA 180868, UG1CA 189867, and U10CA 180822) and by AstraZeneca as part of an alliance between AstraZeneca and MSD. Provision of olaparib and placebo was from AstraZeneca.

ImportanceBiomarkers to guide the use of pertuzumab in the treatment of early-stage ERBB2 (formerly HER2)-positive breast cancer beyond simple ERBB2 status are needed.ObjectiveTo determine if use of the HER2DX genomic assay (Reveal Genomics) in pretreatment baseline tissue samples of patients with ERBB2-positive breast cancer is associated with response to neoadjuvant trastuzumab-based chemotherapy with or without pertuzumab.Design, Setting, and ParticipantsThis is a retrospective diagnostic/prognostic analysis of a multicenter academic observational study in Spain performed during 2018 to 2022 (GOM-HGUGM-2018-05). In addition, a combined analysis with 2 previously reported trials of neoadjuvant cohorts with results from the assay (DAPHNe and I-SPY2) was performed. All patients had stage I to III ERBB2-positive breast cancer, signed informed consent, and had available formalin-fixed paraffin-embedded tumor specimens obtained prior to starting therapy.ExposuresPatients received intravenous trastuzumab, 8 mg/kg, loading dose, followed by 6 mg/kg every 3 weeks in combination with intravenous docetaxel, 75 mg/m2, every 3 weeks and intravenous carboplatin area under the curve of 6 every 3 weeks for 6 cycles, or this regimen plus intravenous pertuzumab, 840 mg, loading dose, followed by an intravenous 420-mg dose every 3 weeks for 6 cycles.Main Outcome and MeasuresAssociation of baseline assay-reported pathologic complete response (pCR) score with pCR in the breast and axilla, as well as association of baseline assay-reported pCR score with response to pertuzumab.ResultsThe assay was evaluated in 155 patients with ERBB2-positive breast cancer (mean [range] age, 50.3 [26-78] years). Clinical T1 to T2 and node-positive disease was present in 113 (72.9%) and 99 (63.9%) patients, respectively, and 105 (67.7%) tumors were hormone receptor positive. The overall pCR rate was 57.4% (95% CI, 49.2%-65.2%). The proportion of patients in the assay-reported pCR-low, pCR-medium, and pCR-high groups was 53 (34.2%), 54 (34.8%), and 48 (31.0%), respectively. In the multivariable analysis, the assay-reported pCR score (as a continuous variable from 0-100) showed a statistically significant association with pCR (odds ratio [OR] per 10-unit increase, 1.43; 95% CI, 1.22-1.70; P P P P = .77). A statistically significant interaction between the assay-reported pCR score and the effect of pertuzumab in pCR was observed.Conclusions and RelevanceThis diagnostic/prognostic study demonstrated that the genomic assay predicted pCR following neoadjuvant trastuzumab-based chemotherapy with or without pertuzumab. This assay could guide therapeutic decisions regarding the use of neoadjuvant pertuzumab.

Purpose:This phase II study investigated daily or weekly sapanisertib (a selective dual inhibitor of mTOR complexes 1 and 2) in combination with fulvestrant.Patients and Methods:Postmenopausal women with estrogen receptor–positive (ER+)/HER2-negative (HER2−) advanced or metastatic breast cancer following progression during/after aromatase inhibitor treatment were randomized to receive fulvestrant 500 mg (28-day treatment cycles), fulvestrant plus sapanisertib 4 mg daily, or fulvestrant plus sapanisertib 30 mg weekly, until progressive disease, unacceptable toxicity, consent withdrawal, or study completion.Results:Among 141 enrolled patients, baseline characteristics were balanced among treatment arms, including prior cyclin-dependent kinase-4/6 (CDK4/6) inhibitor treatment in 33% to 35% of patients. Median progression-free survival (PFS; primary endpoint) was 3.5 months in the single-agent fulvestrant arm, compared with 7.2 months for fulvestrant plus sapanisertib daily [HR, 0.77; 95% confidence interval (CI), 0.47–1.26] and 5.6 months for fulvestrant plus sapanisertib weekly (HR, 0.88; 95% CI, 0.53–1.45). The greatest PFS benefits were seen in patients who had previously received CDK4/6 inhibitors. The most common adverse events were nausea, vomiting, and hyperglycemia, all occurring more frequently in the combination therapy arms. Treatment discontinuation due to adverse events occurred more frequently in the two combination therapy arms than with single-agent fulvestrant (32% and 36% vs. 4%, respectively).Conclusions:Fulvestrant plus sapanisertib daily/weekly resulted in numerically longer PFS in patients with ER+/HER2− advanced or metastatic breast cancer, compared with single-agent fulvestrant. The combination was associated with increased toxicity. Further development of sapanisertib using these dosing schedules in this setting is not supported by these data.

Supplementary Figure from Sapanisertib plus Fulvestrant in Postmenopausal Women with Estrogen Receptor–Positive/HER2-Negative Advanced Breast Cancer after Progression on Aromatase Inhibitor

Background: HER2 mutations are oncogenic drivers in a subset of metastatic breast cancers (MBC). Neratinib (N) is an oral, irreversible pan-HER tyrosine kinase inhibitor with preclinical and clinical activity against HER2 mutations. Genomic analyses from paired biopsies following N ± fulvestrant (F) suggest that resistance to N may occur via amplification of the mutant allele or by acquisition of secondary HER2 mutations. Addition of trastuzumab (T) to N+F showed encouraging clinical activity with durable responses in the SUMMIT trial in hormone receptor-positive (HR+), HER2-mutant MBC, including patients (pts) who had previously received cyclin-dependent kinase 4 & 6 inhibitors (CDK4/6i) [Jhaveri et al. SABCS 2020]. On the basis of these findings, and in order to better understand the contribution of N to the activity of the N+F+T combination, SUMMIT has recently been expanded to include a randomized Simon 2-stage comparison of N+F+T vs. F+T vs. F in pts with HR+, HER2-mutated, HER2-negative MBC who were exposed to CDK4/6i. Enrollment for stage 1 is now complete (N+F+T, n=7; F+T, n=7; F, n=7), and results will be forthcoming once the data are mature. Here we report updated findings from the breast cancer cohorts of the SUMMIT trial for which data are currently available. Methods: The phase 2 SUMMIT trial (NCT01953926) enrolled pts with HR+, HER2-negative MBC whose tumors harbored activating HER2 mutation(s) identified by genomic sequencing. Prior to starting the randomized portion of the trial, these patients were enrolled in a non-randomized cohort and received N+F+T (oral N 240 mg/d, i.m. F 500 mg d1&15 of cycle 1 then q4w, i.v. T 8 mg/kg initially then 6 mg/kg q3w). Following initiation of the randomized portion of the trial, these pts received N+F+T, F+T or F (1:1:1 ratio; dose schedules as above). Pts with HER2-mutant triple-negative breast cancer (TNBC) were enrolled in a non-randomized cohort and received N+T (dose schedules as above). Loperamide prophylaxis was mandatory during the first 2 treatment cycles. There was no restriction on the number of prior lines of systemic therapy for MBC. Efficacy endpoints: investigator-assessed objective response rate and clinical benefit rate (RECIST v1.1 or other defined criteria); duration of response; best overall response. Results: Prior to enrolling the randomized cohort, 24 pts with HR+, HER2-mutated MBC who had previously received CDK4/6i were enrolled in the non-randomized cohort and received N+F+T, and 17 pts with HER2-mutant TNBC were enrolled and received N+T, as of 18-Jun-2021. Data for randomized pts are not yet mature. HER2 allelic variants across both cohorts (pts may have >1 mutation): kinase domain hotspots (n=26); exon-20 insertion (n=9); extracellular domain hotspot (n=4); exon-19 deletion (n=1); transmembrane domain missense (n=1); kinase domain non-hotspot (n=2). Efficacy findings are reported in the Table. Diarrhea was the most commonly reported adverse event: N+F+T (non-randomized cohort), 96%; N+T (TNBC cohort), 94%. No grade 4 diarrhea was reported. Conclusions: N+F+T is a promising combination for pts with HR+, HER2-mutated MBC with prior exposure to CDK4/6 inhibitors. N+T also showed encouraging activity in HER2-mutated TNBC. The first results from the randomized comparison of N+F+T vs. F+T vs. F in pts with HR+, HER2-mutated MBC (Simon stage 1 analysis) will be presented at the meeting. Table: Efficacy findingsHR+, HER2-mutated, HER2-non-amplified MBCHER2-mutant TNBCN+F+T (n=24)N+T (n=17)Confirmed objective response,a n (%)11 (46)5 (29)CR0 (0)1 (6)PR11 (46)4 (24)ORR, % (95% CI)46 (26–67)29 (10–56)Best overall response, n (%)13 (54)7 (41)CR0 (0)1 (6)PR13 (54)6 (35)Best overall response rate, % (95% CI)54 (33–74)41 (18–67)Medianb DOR, months (95% CI)14.4 (6.4–NR)NRClinical benefit, n (%)14 (58)6 (35)CR or PR11 (46)5 (29)SD ≥24 weeks3 (13)1 (6)CBR,b % (95% CI)58 (37–78)35 (14–62)aORR defined as either a CR or PR confirmed no less than 4 weeks after the response criteria are met; bCBR defined as confirmed CR or PR or SD for ≥24 weeks. Note: Tumor response is based on investigator tumor assessments per RECIST v1.1 for HR+, HER2-mutated cohort, and RECIST v1.1 or modified PERCIST for HER2-mutated TNBC cohort. CBR, clinical benefit rate; CI, confidence interval; CR, complete response; DOR, duration of response; F, fulvestrant; HR+, hormone receptor-positive; MBC, metastatic breast cancer; N, neratinib; NR, not reached; ORR, objective response rate; PERCIST, Positron Emission Tomography Response Criteria in Solid Tumors; PR, partial response; RECIST, Response Evaluation Criteria in Solid Tumors; SD, stable disease; T, trastuzumab, TNBC, triple-negative breast cancer. Citation Format: Komal Jhaveri, Haeseong Park, James Waisman, Jonathan W Goldman, Angel Guerrero-Zotano, Valentina Boni, Barbara Haley, Ingrid A Mayer, Adam Brufsky, Eddy S Yang, José A García-Sáenz, François-Clement Bidard, John Crown, Bo Zhang, Aimee Frazier, Irmina Diala, Lisa D Eli, Brian Barnett, Hans Wildiers. Neratinib + fulvestrant + trastuzumab for hormone receptor-positive, HER2-mutant metastatic breast cancer and neratinib + trastuzumab for triple-negative disease: Latest updates from the SUMMIT trial [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr GS4-10.

Background: Neratinib (NERLYNX®), an irreversible pan-HER tyrosine kinase inhibitor, is approved for the extended adjuvant treatment of early-stage HER2+ breast cancer following adjuvant trastuzumab-based therapy and in combination with capecitabine for HER2+ metastatic breast cancer. Diarrhea is the most frequently reported on-target side effect associated with neratinib; in the ExteNET adjuvant trial, where no mandatory anti-diarrheal prophylaxis was used, 39.8% of patients reported grade 3 diarrhea and 16.8% of patients discontinued neratinib due to diarrhea. The CONTROL trial (Clinicaltrials.gov: NCT02400476) was designed to investigate pre-emptive antidiarrheal prophylaxis (loperamide alone or in combination with budesonide or colestipol) or neratinib dose escalation (DE) for the prevention of neratinib-associated diarrhea. Data for the loperamide, budesonide and colestipol cohorts have been reported previously [Barcenas et al. Ann Oncol 2020]. The final findings for the two DE regimen cohorts are reported here. Methods: CONTROL is an international, multi-cohort, open-label, phase 2 study. Patients ≥18 years of age with stage I-IIIc HER2+ breast cancer received oral neratinib (240 mg/day for 1 year) after trastuzumab-based adjuvant therapy. Patients were enrolled sequentially into separate cohorts investigating: 1) mandatory loperamide prophylaxis; 2) budesonide + loperamide; 3) colestipol + loperamide; 4) colestipol + loperamide PRN; 5) neratinib DE + loperamide PRN (two cohorts). DE1 schedule: neratinib 120 mg/day for week 1, 160 mg/day for week 2, then 240 mg/day from week 3 onwards to complete 12 months of treatment. DE2 schedule: neratinib 160 mg/day for weeks 1&2, 200 mg/day for weeks 3&4, then 240 mg/day from week 5 onwards up to 12 months. Both DE cohorts included loperamide PRN. Adverse events were graded according to NCI-CTCAE v4.0. Primary endpoint: incidence of grade ≥3 diarrhea. Results: A total of 563 patients were enrolled in CONTROL. All preventive strategies reduced the incidence of grade 3 diarrhea compared with that seen in ExteNET (historical control: 39.8%). Median cumulative duration of grade 3 diarrhea ranged from 2-3.5 days across the CONTROL study cohorts for the entire 12-month treatment period (compared with 5.0 days for ExteNET). The proportion of patients discontinuing neratinib because of diarrhea was decreased in all cohorts compared with ExteNET (16.8%), except for loperamide alone. Adoption of neratinib DE, particularly the 2-week DE schedule (DE1), most markedly reduced the incidence, severity, and duration of neratinib-associated diarrhea in CONTROL compared with ExteNET (see Table). Conclusions: Neratinib DE + loperamide PRN during the first 2 weeks of treatment (DE1 cohort) was associated with the lowest rates of grade 3 diarrhea (13.3%) and diarrhea-related discontinuations (3.3%) compared with all other anti-diarrheal strategies investigated in CONTROL. These final findings from the study show improved tolerability of neratinib with all diarrhea prophylaxis strategies and suggest that neratinib DE1 with loperamide PRN allows patients to stay on treatment longer and receive the full benefit of neratinib therapy. Table. Patient disposition and diarrhea characteristics: ExteNET vs CONTROL DE cohortsExteNET(n=1408)CONTROL DE1 (n=60)CONTROL DE2 (n=62)Patients completing 1 year of neratinib treatment, %617874Median duration of treatment, months (range)11.6 (2.5–11.9)12.0 (0.2–12.4)11.9 (0.3–14.5)Diarrhea, %Grade 339.813.327.4Grade 4 Citation Format: Arlene Chan, Manuel Ruiz-Borrego, Gavin Marx, Adam Brufsky, Jo Chien, Michael Thirlwell, Maureen Trudeau, Ron Bose, José A García-Sáenz, Daniel Egle, Barbara Pistilli, Johanna Wassermann, Kerry A Cheong, Christian F Singer, Daniel Hunt, Navid Foruzan, Leanne McCulloch, Carlos H Barcenas. Final findings from the CONTROL trial of diarrheal prophylaxis or neratinib dose escalation on neratinib-associated diarrhea and tolerability in patients with HER2+ early-stage breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-18-02.

Background: In high-risk hormone-receptor (HR)+/HER2- BC patients germline (g) mutations can be found in approximately 14% in BRCA1/2 and in BRCA1/2 and other BC predisposition genes in 20% (Pohl-Rescigno E, et al. JAMA Oncol 2020). In metastatic BC CDK4/6 inhibitors may have greater activity in patients with a BRCA mutation detected in ctDNA (André F, et al. J Clin Oncol 2020). The PENELOPE-B trial did not to show an improved invasive disease-free survival (iDFS) by adding palbociclib to ET in high-risk HR+/HER2- BC (Loibl S, et al. J Clin Oncol 2021). Methods: Blood samples from 898 of 1250 PENELOPE-B patients were available. 445 patients were sampled following a case-cohort design (220 cases defined as patients with any event during follow-up and 225 randomly selected patients without any event [non-cases]) and analyzed for germline variants in BRCA1/2 and 16 non-BRCA1/2 cancer predisposition genes (ATM, BARD1, BRIP1, CDH1, CHEK2, FANCM, MRE11A, NBN, PALB2, PTEN, RAD50, RAD51C, RAD51D, STK11, TP53, XRCC2) by targeted next generation sequencing (NGS). The primary definition of mutational status was the prevalence of a pathogenic mutation (mt) in one or more analyzed BC predisposition genes. Statistical analyses for time-to-event endpoints (iDFS, distant disease-free survival [DDFS], and overall survival [OS]) were based on inverse probability weighting: weighted Cox proportional hazard models and Kaplan-Meier estimates were used. Results: 442 of 445 patients (placebo arm: 104 cases and 105 non-cases; palbociclib arm: 114 cases and 119 non-cases) were successfully analyzed for mutational status. A total of 42 (9.5%) patients (placebo arm: 9.1%; palbociclib arm: 9.9%) carried any mutation. 15 (3.4%) patients had a gBRCA1/2 mt (one of whom carried a gATM mt and one a gCHEK2 mt in addition to gBRCA2 mt) and 29 (6.6%) had mutations in one of the other BC predisposition genes (n=8 CHEK2, n=7 PALB2, n=5 ATM, n=2 RAD50, n=1 for BARD1, FANCM, MRE11A, RAD51C, RAD51D, TP53 and n=1 both RAD51D and BRIP1). The mutational status with respect to all genes analyzed showed no significant correlation to clinical baseline variables. With regard to gBRCA1 and gBRCA2 genes only, the mutational status significantly correlated with age but not with other clinical variables: all 15 (100%) gBRCA mt carriers were younger than 50 years compared to 238 (56%) wildtype (wt) patients (p=0.002). The iDFS rate after 3 years was 80.9% in patients with any mutation and 79.5% in patients without. Mutational status (mt vs. wt) based on all genes analyzed was not prognostic (iDFS: hazard ratio 1.015, 95%CI 0.558-1.784; DDFS: 0.970, 95%CI 0.521-1.758; OS: 0.768, 95%CI 0.274-1.615). Neither the mutated patients had a benefit from palbociclib treatment (palbociclib vs placebo; iDFS: hazard ratio 0.766, 95%CI 0.263-3.022; DDFS: 0.897, 95%CI 0.275-3.489; OS: 0.666, 95%CI 0.063-5.671) nor the wt patients (iDFS: hazard ratio 0.918, 95%CI 0.650-1.303; DDFS: 0.966, 95%CI 0.679-1.393; OS: 0.901, 95%CI 0.573-1.433); interaction tests for treatment arm/mutational status for all time-to-event endpoints were not statistically significant. Analysis in the subgroups of patients by gBRCA1/2 showed similar results but had less statistical power. Conclusions: In this case-cohort analysis of 442 patients enrolled in the PENELOPE-B trial, the detection of BC predisposition genes was lower than expected with 10%. This is probably due to the low rate of gBRCA1/2 carriers (3.4%), which could be influenced by the selection criteria of the trial. Patients with gBRCA1/2 or other BC disposition genes had a comparable outcome to non-carriers in the PENELOPE-B trial. Citation Format: Sibylle Loibl, Jan Hauke, Karen Gelmon, Frederik Marmé, Corinna Ernst, Miguel Martin, Michael Untch, Hervé Bonnefoi, Erik Knudsen, Seock-Ah Im, Angela DeMichele, Laura Van’t Veer, Sung-Bae Kim, Harry Bear, Nicole McCarthy, Nicholas Turner, Agnieszka Witkiewicz, Federico Rojo, Peter A Fasching, José A García-Sáenz, Catherine M Kelly, Toralf Reimer, Masakazu Toi, Hope S Rugo, Carsten Denkert, Michael Gnant, Andreas Makris, Yuan Liu, Olga Valota, Bärbel Felder, Karsten Weber, Valentina Nekljudova, Eric Hahnen. Germline BRCA1/2 and other predisposition genes in high-risk early-stage HR+/HER2- breast cancer (BC) patients treated with endocrine therapy (ET) with or without palbociclib: A secondary analysis from the PENELOPE-B study [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-13-36.

Cardiotoxicity due to anthracyclines (CDA) affects cancer patients, but we cannot predict who may suffer from this complication. CDA is a complex disease whose polygenic component is mainly unidentified. We propose that levels of intermediate molecular phenotypes in the myocardium associated with histopathological damage could explain CDA susceptibility; so that variants of genes encoding these intermediate molecular phenotypes could identify patients susceptible to this complication. A genetically heterogeneous cohort of mice generated by backcrossing (N = 165) was treated with doxorubicin and docetaxel. Cardiac histopathological damage was measured by fibrosis and cardiomyocyte size by an Ariol slide scanner. We determine intramyocardial levels of intermediate molecular phenotypes of CDA associated with histopathological damage and quantitative trait loci (ipQTLs) linked to them. These ipQTLs seem to contribute to the missing heritability of CDA because they improve the heritability explained by QTL directly linked to CDA (cda-QTLs) through genetic models. Genes encoding these molecular subphenotypes were evaluated as genetic markers of CDA in three cancer patient cohorts (N = 517) whose cardiac damage was quantified by echocardiography or Cardiac Magnetic Resonance. Many SNPs associated with CDA were found using genetic models. LASSO multivariate regression identified two risk score models, one for pediatric cancer patients and the other for women with breast cancer. Molecular intermediate phenotypes associated with heart damage can identify genetic markers of CDA risk, thereby allowing a more personalized patient management. A similar strategy could be applied to identify genetic markers of other complex trait diseases.

Simple Summary There is insufficient evidence on the impact of sociodemographic and clinical factors on health-related lifestyles in breast cancer (BC) survivors. The International guidelines for cancer prevention are recommended not only for the general population but also for people who already have cancer. We sought to explore the degree of adherence to 2018 WCRF/AICR cancer prevention recommendations and to identify potentially influential factors, in 420 BC survivors in Spain. Global adherence was moderate, higher for the consumption of fruits and vegetables and lower for limiting red/processed meat consumption and having a high fibre intake. Compliance was worse in more educated survivors and in women with first-degree relatives with BC. There were differences in compliance with specific recommendations according to sociodemographic and clinical characteristics. This information is of interest to promote behavioural changes towards healthier lifestyles in BC survivors. Breast cancer (BC) survivors are advised to follow the WCRF/AICR cancer prevention recommendations, given their high risk of developing a second tumour. We aimed to explore compliance with these recommendations in BC survivors and to identify potentially associated clinical and sociodemographic factors. A total of 420 BC survivors, aged 31-80, was recruited from 16 Spanish hospitals. Epidemiological, dietary and physical activity information was collected through questionnaires. A 7-item score to measure compliance with the recommendations was built according to the 2018 WCRF/AICR scoring criteria. Standardized prevalences and standardized prevalence ratios of moderate and high compliance across participant characteristics were estimated using multinomial and binary logistic regression models. The mean score was 3.9 (SD: 1.0) out of 7 points. Recommendations with the worst adherence were those of limiting consumption of red/processed meats (12% of compliance, 95% CI: 8.2-15.0) and high fibre intake (22% of compliance, 95% CI: 17.6-27.0), while the best compliance was observed for the consumption of fruits and vegetables (73% of compliance, 95% CI: 69.2-77.7). Overall, adherence was worse in women with university education and in those with first-degree relatives with BC. This information may be of interest to design and implement personalized preventive measures adapted to the characteristics of these patients.

Background: Predict Breast (www.predict.nhs.uk) is an online prognostication and treatment benefit tool for early invasive breast cancer. The aim of this study was to incorporate the prognostic effect of progesterone receptor (PR) status into a new version of PREDICT and to compare its performance to the current version (2.2).Method: The prognostic effect of PR status was based on the analysis of data from 45,088 European patients with breast cancer from 49 studies in the Breast Cancer Association Consortium. Cox proportional hazard models were used to estimate the hazard ratio for PR status. Data from a New Zealand study of 11,365 patients with early invasive breast cancer were used for external validation. Model calibration and discrimination were used to test the model performance.Results: Having a PR-positive tumour was associated with a 23% and 28% lower risk of dying from breast cancer for women with oestrogen receptor (ER)-negative and ER-positive breast cancer, respectively. The area under the ROC curve increased with the addition of PR status from 0.807 to 0.809 for patients with ER-negative tumours (p = 0.023) and from 0.898 to 0. 902 for patients with ER-positive tumours (p = 2.3 x 10(-6)) in the New Zealand cohort. Model calibration was modest with 940 observed deaths compared to 1151 predicted.Conclusion: The inclusion of the prognostic effect of PR status to PREDICT Breast has led to an improvement of model performance and more accurate absolute treatment benefit predic-tions for individual patients. Further studies should determine whether the baseline hazard function requires recalibration. (C) 2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Background: Molecular plasticity of breast cancer is crucial for the development of therapy-resistant disease. In this investigation, we studied changes in molecular signatures between pretherapeutic (pre-Tx) and post-therapeutic (post-NACT) tumor samples from patients included in the PENELOPE-B (NCT01864746) trial. The phase III PENELOPE-B study did not show a significant benefit from palbociclib in women with centrally confirmed HR+, HER2- primary breast cancer without a pathological complete response after taxane-containing neoadjuvant chemotherapy (NACT) and at high-risk of relapse (CPS-EG score ≥3 or 2 and ypN+) (Loibl et al. JCO 2021). However, first translational investigations showed that a small number of patients with a luminal-B tumor subtype, based on absolute intrinsic molecular subtyping (AIMS, Paquet & Hallet, JNCI 2014) subtyping after NACT, had a numerical benefit from post-NACT palbociclib. We have therefore extended the analysis and included a cohort of paired pre-Tx and post-NACT samples. Methods: We investigated gene expression in pre-Tx (n=259) tumor tissue samples using the HTG EdgeSeq Oncology Biomarker Panel including 2549 genes (HTG Molecular Diagnostics Inc.); for the same patients the same panel on post-NACT residual tumor samples were available. The paired samples were selected based on a case-cohort approach. Based on 91 genes of this panel, the AIMS subtype was calculated. In addition, we performed exploratory biomarker analyses to identify genes and gene signatures with prognostic and predictive relevance. After completion of NACT, PENELOPE-B patients were randomized to palbociclib versus placebo in addition to standard endocrine therapy. Results: The prevalence of AIMS subtypes, in particular LumA vs LumB, changed in pre-Tx and post-NACT tumors. In the pre-Tx samples, 115 (44%) and 123 (47%) of tumors had LumA and LumB subtypes, respectively, as expected from a high-risk cohort. However, in the post-NACT samples, LumA tumors were predominant (n=183, 71%) over LumB (n=30; 12%). 78 (30%) and 6 (2%) tumors switched their subtype from LumB to LumA and LumA to LumB, respectively. For further analyses, we compared the groups of low proliferating (LumA and NormL) and high proliferating subtypes (LumB, BasalL and HER2E). In bivariable Cox regression analysis, the grouped pre-Tx and post-NACT AIMS subtypes were independent prognostic factors for iDFS: HR=1.85 (1.16-2.98, p=0.011) for pre-Tx LumB/BasalL/HER2E vs LumA/NormL and HR=2.18 (1.24-3.84, p=0.007) for post-NACT. Similar results were found when adjusted for prognostic clinical factors and for DDFS and OS endpoints although the pre-Tx subtype did not reach significance. These and further Cox models investigating interaction effects show that patients with tumors developing from high (pre-Tx) to low proliferation (post-NACT) had a higher iDFS risk compared to stable low proliferating tumors but a lower iDFS risk compared to stable high proliferating tumors. Neither in the pre-Tx LumB/BasalL/HER2E nor in the pre-Tx LumA/NormL subgroup a benefit from palbociclib was observed. Based on the results of the AIMS subtyping, we extended the exploratory analysis to identify genes that might be involved in the prognostic and predictive effects as well as genes driving the subtype switch. The analysis is ongoing and the relevant genes will be presented at the conference. Conclusions: Our findings show that the switch from high-risk molecular subtypes (in particular LumB) to low-risk subtypes (in particular LumA) is common in neoadjuvant therapy of luminal tumors. The adaptation of luminal high-risk tumors to therapy-induced stress is crucial for the clinical outcome and the results suggest that molecular defined tumor subtypes might not be as stable as originally thought. Citation Format: Carsten Denkert, Frederik Marmé, Miguel Martin, Michael Untch, Hervé Bonnefoi, Sung-Bae Kim, Harry Bear, Agnieszka Witkiewicz, Seock-Ah Im, Angela DeMichele, Laura Van’t Veer, Nicole McCarthy, Thorsten Stiewe, Karen A. Gelmon, José A. García-Sáenz, Catherine M. Kelly, Toralf Reimer, Erik Knudsen, Nicholas Turner, Federico Rojo, Peter A. Fasching, Julia Teply-Szymanski, Yuan Liu, Masakazu Toi, Hope S. Rugo, Michael Gnant, Andreas Makris, Bärbel Felder, Karsten Weber, Sibylle Loibl. Molecular plasticity of luminal breast cancer and response to CDK 4/6 inhibition - The biomarker program of the PENELOPE-B trial investigating post-neoadjuvant palbociclib [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr PD2-04.

Background: It is not known whether modifiable lifestyle factors that predict survival after invasive breast cancer differ by subtype. Methods: We analyzed data for 121,435 women diagnosed with breast cancer from 67 studies in the Breast Cancer Association Consortium with 16,890 deaths (8,554 breast cancer specific) over 10 years. Cox regression was used to estimate associations between risk factors and 10-year all-cause mortality and breast cancer–specific mortality overall, by estrogen receptor (ER) status, and by intrinsic-like subtype. Results: There was no evidence of heterogeneous associations between risk factors and mortality by subtype (Padj > 0.30). The strongest associations were between all-cause mortality and BMI ≥30 versus 18.5–25 kg/m2 [HR (95% confidence interval (CI), 1.19 (1.06–1.34)]; current versus never smoking [1.37 (1.27–1.47)], high versus low physical activity [0.43 (0.21–0.86)], age ≥30 years versus 0– Conclusions: We confirm associations between modifiable lifestyle factors and 10-year all-cause mortality. There was no strong evidence that associations differed by ER status or intrinsic-like subtype. Impact: Given the large dataset and lack of evidence that associations between modifiable risk factors and 10-year mortality differed by subtype, these associations could be cautiously used in prognostication models to inform patient-centered care.

Background: In the SUMMIT trial, original cohorts of patients with HR+, HER2-negative (locally assessed), HER2-mutant MBC received N alone or N+F, with promising clinical response rates but abbreviated duration. Clinical progression coincided with emergence of additional HER2 mutations and/or amplification of the mutant allele [Smyth et al. Cancer Discov 2020;10:198–213]. Addition of T to the combination was postulated to prolong response; the combination of N+F+T in heavily pretreated patients with HR+, HER2-mutant MBC who had received CDK4/6 inhibitors (n=51) yielded a confirmed overall response rate (ORR) of 35.3%, median duration of response (DOR) of 14.3 months, clinical benefit rate (CBR) of 47.1%, and median progression-free survival (PFS) of 8.2 months [Jhaveri et al. J Clin Oncol 2022;40:1028]. Seven of these 51 patients were part of a randomized (1:1:1) cohort who received N+F+T, F+T, or F alone. Patients randomized to F+T or F could crossover to N+F+T upon progression. No patients responded to F or F+T; however, one of four patients who crossed over to N+F+T upon progression on F+T responded to the triplet, as did two of six who crossed over upon progression on F. We undertook ctDNA sequencing in patients who responded to N+F+T upfront and after crossover. Methods: Patients with HR+, HER2-negative MBC with activating HER2 mutation(s) and prior CDK4/6i received N+F+T (oral N 240 mg/d with loperamide prophylaxis, im F 500 mg d1, d15, and d29 of cycle 1 then q4w, iv T 8 mg/kg initially then 6 mg/kg q3w) or F+T or F alone. Efficacy endpoints included investigator-assessed ORR and CBR (RECIST v1.1), DOR, and best overall response. ctDNA was collected at baseline, every third cycle during treatment, and at the end of treatment and analyzed by next-generation sequencing. Samples were analyzed using the TEMPUS xF assay. Results: Sequencing results from ctDNA analysis are pending at the time of this abstract submission. Baseline HER2 mutations and co-alterations will be reported and compared with those found in tissue samples. Genomic spectrum and variant allele frequencies in samples taken at baseline, on treatment, and at the end of treatment from patients who experienced complete or partial response to N+F+T and then progressed (n=25) will be sequenced and mechanisms of acquired resistance will be posited. ctDNA genomic profiles of serial time points from patients randomized to F or F+T before and after crossover to N+F+T (n=10) will also be evaluated. Conclusions: Similarities and differences between the mechanisms of acquired resistance to N+F+T, and those previously reported to be associated with progression on N or N+F, will be discussed. Citation Format: Cynthia Ma, James Waisman, Adam M. Brufsky, Eddy S. Yang, Hans Wildiers, John P. Crown, Sarina A. Piha-Paul, Jennifer M. Suga, José Ángel García-Sáenz, Valentina Gambardella, Angel Guerrero, Salomon Stemmer, Ron Bose, Tonya Novara-Demgen, Daniel DiPrimeo, Lisa D. Eli, Komal Jhaveri. Genomic analysis of circulating tumor DNA (ctDNA) from patients with HR+, HER2-mutant metastatic breast cancer (MBC) enrolled in SUMMIT: mechanisms of acquired resistance to neratinib + fulvestrant + trastuzumab (N+F+T) [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD17-01.

Background: HER2DX (Prat et al. EBiomedicine 2022) is a 27-gene prognostic (risk-score) and predictive (pathological complete response [pCR]-score) assay in early-stage HER2+ breast cancer based on clinical data and the expression of 4 gene signatures (immune, proliferation, luminal differentiation and HER2 amplicon). Here, we aim to evaluate, for the first time, the ability of HER2DX to predict pCR following neoadjuvant TCH or TCHP in HER2+ disease. Methods: Standardized HER2DX was performed in a central lab on baseline pre-treatment FFPE tumor biopsies from the GOM-HGUGM-2018-05 study in Spain, a consecutive retrospective series of patients (pts) with newly diagnosed stage I-III HER2+ breast cancer eligible for neoadjuvant therapy. Pts received standard 6 cycles of docetaxel, carboplatin and trastuzumab (TCH) or TCH with pertuzumab (TCHP) regimens. Primary aim was to test the ability of HER2DX pCR score to predict pCR (ypT0/is ypN0). Secondary objectives were to test the ability of HER2DX pCR score to predict pCR independently of clinical-pathological variables and the PAM50 subtype (HER2-enriched versus not), and to evaluate the association of HER2DX pCR score with the HER2DX risk-score. Logistic regression and receiver-operator curve (ROC) analysis were assessed. Statistical analyses were performed in R code 4.0.5. Results: HER2DX was evaluated in 155 pts (97%) enrolled in the study with available RNA (as of June 2022). Mean age of pts was 50 (range 22-74) and 55.2% of pts (n=85) were pre-menopausal. Clinical T2-4 disease represented 77.4% of cases (n=120), clinical node-positive disease (cN1-3) represented 63.9% of cases (n=99), and 68.0% of tumors (n=105) were hormone receptor-positive. The overall pCR rate was 57.4% (95% confidence interval [CI] 50-65): 52.2% (95% CI 40-64) with TCH (n=67) and 61.4% (95% CI 50-72) with TCHP (n=88). The proportion of HER2DX low-, medium- and high-pCR groups was 34.2%, 34.8% and 31.0%, respectively. HER2DX pCR score (as a continuous variable from 0 to 100) was significantly associated with pCR (odd ratio [OR]=1.03, p=5.91e-07). The pCR rates in HER2DX pCR-high and pCR-low groups were 75.0% and 28.0% (OR=7.6, 95% CI 3.2-19.1, p=7.14e-06), respectively. In pts treated with TCHP, the pCR rates in HER2DX pCR-high and pCR-low groups were 85.7% and 27.3% (OR=16.0, 95% CI 4.3-59.01, p=3.2e-05), respectively. The AUC ROC of HER2DX pCR score (as a continuous variable) and pCR status was 0.746 (in all pts) and 0.812 (in pts treated with TCHP). HER2DX pCR score was significantly associated with pCR independently of hormone receptor status, Ki67, age, menopausal status, pertuzumab use, clinical stage and PAM50 HER2-enriched subtype. The proportion of HER2DX low- and high-risk of relapse disease was 32.0% and 68.0%, respectively. The correlation of HER2DX pCR score and HER2DX risk-score was weak (coefficient=-0.17), as previously described. Proportion of cases according to both HER2DX scores and absolute difference of pCR rates between TCHP and TCH in each combined group is shown in Table. Conclusion: The HER2DX genomic test predicts pCR following neoadjuvant TCH or TCHP regimens independently of clinical-pathological variables and intrinsic subtype. The combination of both HER2DX scores might help better tailor systemic therapy in patients with newly diagnosed stage I-III HER2+ breast cancer. Citation Format: Coralia Bueno-Muiño, Isabel Echavarria, Sara López-Tarruella, Roche-Molina Marta, María del Monte-Millán, Tatiana Massarrah, Yolanda Jerez Gilarranz, Blanca Herrero, Salvador Gámez, Iván Márquez-Rodas, María Cebollero-Presmanes, Nevado Santos Manuel, Pilar de la Morena Barrio, Francisco Ayala de la Peña, José Ángel García-Sáenz, Fernando Moreno Antón, Álvaro Rodríguez Lescure, Teresa Quintanar, Diego Malón-Giménez, Laura Rodriguez-Lajusticia, Ana Isabel Ballesteros García, Dulce Bañón Torres, Lucía Villarejo, Nerea Lobato, Ainhoa Arias, Inmaculada Ocaña, Enrique Álvarez, Laia Paré, Mercedes Marín-Aguilera, Patricia Galván, Fara Brasó-Maristany, Ana Vivancos, Patricia Villagrasa, Joel S Parker, Charles M. Perou, Aleix Prat, Miguel Martín. Independent validation of the HER2DX genomic test in HER2-positive breast cancer treated with neoadjuvant docetaxel, carboplatin, trastuzumab +/- pertuzumab (TCH/TCHP): a correlative analysis from a multicenter academic study [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-01-46.

Introduction Since the approval a decade ago of everolimus in combination with endocrine therapy (ET), the treatment landscape of metastatic breast cancer (mBC) has changed dramatically. Endocrine monotherapy after progression to CDK4/6 inhibitors has shown a limited progression-free survival (PFS) below 3 months. Evidence of the efficacy of everolimus plus ET after CDK4/6 inhibitors is scarce. Methods We performed a retrospective observational study of patients with mBC treated with everolimus between September 2011 and April 2022 in 4 Spanish hospitals. Clinical and demographic data were collected from medical records. Our main objective was to estimate the median progression-free survival (mPFS) for everolimus + ET in patients previously treated with a CDK4/6 inhibitor. We also collected the adverse events (AE) related to everolimus. Quantitative variables were summarized with medians (range), and qualitative variables with proportions. We used the Kaplan-Meier method for survival estimates. Results We identified a total of 297 mBC patients treated with everolimus plus ET. The median follow-up time was 20 months (interquartile range: 1 – 97 months). In this cohort, the median age at diagnosis was 49 years (26 – 84 years). At the moment of starting everolimus, the median number of previous lines of treatment was 2 (0 – 12), 22% of patients were ‘de novo’ metastatic, 67% presented visceral involvement, 40% had received previous chemotherapy for advanced disease, and 51% (n=152) had received a previous CDK4/6 inhibitor. The ET combined with everolimus was exemestane (77%), fulvestrant (18%), and tamoxifen (5%). 45% of patients were alive at data cut-off. In patients previously treated with a CDK4/6 inhibitor, the estimated median PFS (mPFS) was 5.9 months (95%CI: 5.0 – 7.8 months). In patients without visceral involvement (n=52), mPFS was 7.2 months (95%CI: 5.5 – 11.0 months), and 5.6 months (95%CI: 3.9 – 7.8 months) in the presence of visceral metastasis (n=100). In patients without previous chemotherapy in the metastatic setting (n=109), mPFS was 7.2 months (95%CI: 5.9 – 8.4 months), and 4.6 months (95%CI: 3.1 – 5.7 months) for patients who had received previous chemotherapy (n=43). For patients without a previous CDK4/6 inhibitor (n=145), the median PFS was 8.3 months (95%CI: 6.4 – 10.3 months). Everolimus starting doses were 10 mg (83%), 5 mg (15%), and 7.5 mg (2%). Dexamethasone mouthwash was used by 44% of patients. The most frequent AE were mucositis (51%; 3% grade 3), anemia (41%; 3% grade 3), hyperglycemia (34%; 2% grade 3), rash (28%; 2% grade 3), neumonitis (21%; 2% grade 3), and diarrhea (17%; 1% grade 3). There were no grade 4-5 adverse events. Dose reduction was made in 35% of patients, and in 16% of patients the treatment was discontinued due to toxicity. Conclusions In our cohort, the use of everolimus plus ET in mBC patients previously treated with a CDK4/6 inhibitor showed a clinically significant benefit in terms of PFS, especially in patients without visceral metastasis, and no previous chemotherapy for advanced disease. In this real-world study, the toxicity profile of everolimus was manageable. Citation Format: Rodrigo Sánchez-Bayona, Manuel Alva, Alfonso López de sa, Yolanda Jerez Gilarranz, Ana Sánchez de torre, Pablo Tolosa, Alicia de luna, Sara López-Tarruella, Laura Lema, Fernando Moreno, Isabel Echavarria, Ainhoa Madariaga, Javier Benítez, Blanca Herrero, Macarena Rey, Justo Ortega, Salvador Gámez, Andrea Modrego, Rocío Martín Lozano, Luis Figuero-Pérez, Roberto Jiménez, Marta González Sevilla, Irene González, Marianela Bringas Beranek, María de toro, Tatiana Massarrah, María del Monte-Millán, Marina Pinardo, Luis Manso, Coralia Bueno-Muiño, José Ángel García-Sáenz, Miguel Martín, Eva Ciruelos. A real-world evidence study of everolimus plus endocrine therapy beyond CDK4/6 inhibitors for HR+/HER2- advanced breast cancer. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-01-04.

Background: The Penelope-B trial did not show improvement in invasive disease-free survival (iDFS) with the addition of palbociclib to endocrine therapy (ET) in patients with high-risk early breast cancer (BC) after neoadjuvant chemotherapy (NACT). Biomarkers may be able to identify subgroups of patients deriving benefit from Palbociclib and guide future studies. Estrogen-receptor (ER), progesterone-receptor (PgR) and Ki-67 might be helpful in identifying patients benefiting from palbociclib. Concordantly, tumors with elevated expression of Cyclin D1 and phosphorylated retinoblastoma protein (phospho-RB) may harbor more dependency on CDK4/6 and thus higher sensitivity to palbociclib. Methods: The percentage of positive ER and PgR cells and Ki-67 assessed in surgical specimens after NACT were combined to obtain the immunohistochemical score 3 (IHC3, Cuzick et al JCO 2011, low vs high based on the median IHC3 value). Cyclin D1 and phospho-RB Ser 807/811 immunoreactive (phospho-RB) scores were analyzed in residual tumors after NACT (range 0-12 each). Proportional hazard regression model was used to assess the predictive and prognostic value of IHC3 and treatment on iDFS. Subgroup analysis was performed according to BC intrinsic subtypes (luminal-A/normal-like, luminal-B/HER2-enriched/basal) and HER2-status (HER2 0, HER2 low). Cox/Fine-Gray regression was used to define the predictive and prognostic value of CyclinD1 (≤1, >1), phospho-RB (≤2, >2) as dichotomized and continuous variables on iDFS, distant DFS (DDFS), locoregional invasive recurrence-free interval (LRRFI) and overall survival (OS). Multivariate analyses (MVA) were adjusted for age (≤50 vs >50), Ki-67 (≤15 vs >15), region (non-Asian vs Asian), ypN (ypN0-1 vs ypN2-3), risk status (CPS-EG=2 ypN+ vs ≥3), cT (cT1-2 vs cT3-4), ypT (ypT0-2 vs ypT3-4), and grade (G1-2 vs G3). The MVA for IHC3 includes all the covariates above except Ki-67. p< 0.05 was defined as statistically significant. Results: Data for ER, PgR, Ki-67, HER2, Cyclin D1 and phospho-RB were available for 1250 patients. Overall, 98.9% of the patients had ER+ tumors, 75.0% PgR+, 52.2% had HER2 low, 25.5% Ki-67>15, 50% had IHC3 score higher than median, 93.9% had Cyclin D1 >1, 57.8% had phospho-RB >2. Patients with IHC3 score high had a worse iDFS compared to patients with IHC3 score low (MVA HR 2.28 95%CI (1.78-2.91), p< 0.0001). Patients with luminal-A/normal-like tumors and IHC3 low had an improved iDFS with the addition of palbociclib to ET (MVA HR 0.35 95%CI (0.14-0.90), test for interaction p=0.01). No difference was observed according to HER2 status. Cyclin D1>1 has no predictive value but is prognostic for better iDFS (MVA HR 0.62 95%CI (0.41-0.94), p=0.023), LRRFI (MVA HR 0.30 95%CI (0.15-0.63), p=0.001) and OS (MVA HR 0.50 95%CI (0.28-0.89), p=0.019). Similar results were obtained when Cyclin D1 was analysed as a continuous variable. Phospho-RB had neither predictive nor prognostic value. Phospho-RB highly correlates with Ki-67 (p< 0.001, Spearman correlation 0.248). Conclusions: Patients with high Cyclin D1 expression had a favorable prognosis independent of treatment arm, but patients with luminal-A/normal-like tumors and IHC3 low after NACT had an improved outcome when receiving palbociclib in addition to adjuvant ET. Theses exploratory studies suggest specific signatures/phenotypes could predict benefit from Palbociclib in high-risk early breast cancer. Citation Format: Erik S. Knudsen, Sivaramakrishna Rachakonda, Frederik Marmé, Miguel Martín, Michael Untch, Hervé R. Bonnefoi, Wolfgang D. Schmitt, Sung-Bae Kim, Harry D. Bear, Agnieszka Witkiewicz, Seock-Ah Im, Angela DeMichele, Laura Van’t Veer, Nicole McCarthy, Bruno V. Sinn, Karen Gelmon, José Ángel García-Sáenz, Catherine M. Kelly, Toralf Reimer, Nicholas Turner, Federico Rojo, Martin Filipits, Peter A. Fasching, Christian Schem, Lesley-Ann Martin, Yuan Liu, Masakazu Toi, Hope Rugo, Michael Gnant, Andreas Makris, Jenny Furlanetto, Karsten Weber, Carsten Denkert, Sibylle Loibl. Immunohistochemical markers and determinants of clinical response in the Penelope-B trial [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD17-06.

Background: Neratinib (NERLYNX®), an irreversible pan-HER tyrosine kinase inhibitor, is used for the extended adjuvant treatment of patients with early-stage HER2-positive (HER2+) breast cancer following adjuvant trastuzumab-based therapy and for patients with HER2+ metastatic breast cancer in the 3rd-line setting. Diarrhea, particularly in the first 1-2 months, is the main tolerability concern with neratinib and is common in the absence of proactive management. In the ExteNET trial, where no mandatory prophylaxis was used, the rate of grade 3 diarrhea was 40%, 34% of patients experienced at least 1 dose hold, and 17% of patients discontinued due to diarrhea. The CONTROL trial previously showed that pre-emptive antidiarrheal prophylaxis (loperamide alone or in combination with budesonide or colestipol) or dose escalation (DE) reduced the rate, severity, and duration of neratinib-associated grade ≥3 diarrhea compared with ExteNET. Currently, antidiarrheal prophylaxis is initiated with the first dose of neratinib and used during the first 2 cycles of treatment (US PI). Updated findings from two DE cohorts in CONTROL are reported. Methods: CONTROL is an international, multi-cohort, open-label, phase 2 study. Patients ≥18 years with stage I-IIIc HER2+ breast cancer were treated with neratinib (240 mg/day for 1 year) after trastuzumab-based adjuvant therapy. Patients were enrolled sequentially into separate cohorts including 2 dose-escalation cohorts: DE1 (neratinib 120 mg/day on days 1-7, 160 mg/day on days 8-14, then 240 mg/day to day 365) + loperamide as needed (PRN); and DE2 (neratinib 160 mg/day on days 1-14, 200 mg/day on days 15-28, then 240 mg/day to day 365) + loperamide PRN. Adverse events were graded per NCI-CTCAE v4.0. Primary endpoint: incidence of grade ≥3 diarrhea. Data cut-off: May 1, 2020. Results: Complete data for DE1 (60 patients) and interim data for the ongoing DE2 (60 patients) are presented. All patients in DE1 were off study and 40 (66.7%) of patients remained on treatment in the ongoing DE2. The median treatment duration for DE1 was 12.0 months (IQR 11.1-12.0) and for DE2 was 3.7 months (IQR 1.6-9.1). Overall, 48% and 57% of DE1 and DE2 patients, respectively, had prior pertuzumab; 0% and 3%, respectively, had prior T-DM1. The majority of patients in both DE1 and DE2 dose-escalated to 240 mg on planned schedule. The incidence of grade ≥3 diarrhea was 13.3% in DE1 and 20.0% in DE2. The median cumulative duration of grade ≥3 diarrhea over the entire 12-month treatment period was 3 days (range 1-6 days) for DE1 and 2 days (range 1-7 days) for DE2. In both DE1 and DE2, 7 patients (11.7%) had at least one dose hold while on study (none during escalation phase in DE1 and 4 during escalation phase in DE2). In both DE1 and DE2, 2 (3.3%) patients discontinued neratinib because of diarrhea (1 during escalation phase in each cohort). Updated data for the DE2 cohort will be presented. Conclusions: Adoption of neratinib DE reduced the incidence, severity, and duration of neratinib-associated diarrhea in CONTROL compared with ExteNET. DE1 was associated with low rates of dose holds and diarrhea-related discontinuations compared with all previously mandated prophylaxis strategies investigated in CONTROL and with ExteNET. Together these results show improved tolerability of neratinib with DE and suggest that DE combined with loperamide PRN may allow patients to stay on neratinib for the recommended period of time. Neratinib dose escalation scheme 1 (n=60)Neratinib dose escalation scheme 2 (n=60)On neratinib treatment, %066.7Median duration of treatment, months12.03.7Diarrhea, %Grade 140.041.7Grade 245.033.3Grade 313.320.0Grade 400Discontinuation rate due to diarrhea, %3.33.3At least one dose hold due to diarrhea, %11.711.7 Citation Format: Manuel Ruiz-Borrego, Arlene Chan, Gavin Marx, Adam Brufsky, A Jo Chien, Michael Thirlwell, Maureen Trudeau, Ron Bose, José A García-Sáenz, Daniel Egle, Daniel Hunt, Utpal Khambholja, Leanne McCulloch, Naisargee Shah, Debu Tripathy, Carlos H Barcenas, the CONTROL Investigators. Bringing diarrhea under CONTROL: Dose escalation reduces neratinib-associated diarrhea and improves tolerability in HER2-positive early-stage breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS13-20.

Background: TNBC is a particularly aggressive subtype with high recurrence rates and poor long-term survival. Anthracycline-free regimens based on docetaxel plus carboplatin (TCb) achieve around 50-55% pathologic complete responses (pCR) which correlates with better survival outcomes. Identification of genomic predictors of response is key to individualize therapies for this heterogeneous breast cancer (BC) subgroup. FOXA1 is a pioneer factor for androgen (AR) and estrogen receptors (ER). Its under-expression has been linked to cancer stemness in TNBC and better prognosis in ER-positive BC. The differential expression of AR, FOXA1 and BRCA1 is associated with sensitivity to chemotherapy in TNBC patients. Data support the plasticity role of FOXA1 driving basal to luminal BC cells by inducing luminal genes but also by repressing the basal phenotype and thus, tumor aggressiveness, although its role as a biomarker in TNBC is still controversial. We have analyzed RNAseq data of FOXA1 and AR in a series of TNBC tumors homogenously treated with neoadjuvant TCb to study their correlation with survival and response. Methodology: 300 TNBC patients have been included in a multicenter, prospective, non-randomized trial aimed to identify predictors of response to TCb in the neoadjuvant setting (NCT01560663). 278/300 patients were evaluable. PAM50 subtypes (NanoString nCounter) and RNAseq (HiSeq2500) were analyzed for those patients with both available samples and evaluable pathological response (n=208). Correlations were studied by the Kendall method. Linear or logistic regressions were adjusted for univariant analysis depending on numerical or categorical response variables, respectively. Results: FOXA1 and AR were differentially expressed between basal and non-basal tumor subtypes (PAM50), being overexpressed in non-basal (p Citation Format: Sara López-Tarruella, María del Monte-Millán, Enrique Alvarez, Yolanda Jerez, José Ángel García Saenz, Isabel Echavarria, Fernando Moreno, Ivan Márquez-Rodas, Coralia Bueno-Muiño, Blanca Herrero, Maria Cebollero, Rocío Ramos-Medina, Nerea Lobato, Ricardo González del Val, Maria Isabel Palomero, Santiago Lizarraga, Uriel Bohn, Ana Isabel Ballesteros, Patricia Rincón, Tatiana Massarrah, Inmaculada Ocaña, Lucía Villarejo, Charles M Perou, Miguel Martin. Potential value of FOXA1 expression as genomic predictor of response to docetaxel and carboplatin neoadjuvant (NA) chemotherapy in patients with triple negative breast cancer (TNBC) [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS4-12.

Background: HER2 mutations are oncogenic in hormone receptor positive (HR+) metastatic breast cancer (MBC), and may confer resistance to prior endocrine therapy but retain sensitivity to neratinib. Neratinib is an oral, irreversible, pan-HER tyrosine kinase inhibitor with clinical activity either as a single agent or in combination with fulvestrant in HER2-mutated, HER2-non-amplified MBC. Genomic analyses suggest that acquired resistance to neratinib can occur via additional HER2 alterations, which may alter HER2-pathway signaling. We investigated whether dual HER2-targeted therapy could improve clinical benefit in a cohort of patients with HER2-mutant, HR+ MBC treated with neratinib + trastuzumab + fulvestrant (N+T+F) from SUMMIT - a phase 2 basket trial (NCT01953926). Methods: Patients with HR+ MBC with known or suspected pathogenic HER2 mutation(s) identified by genomic sequencing were eligible to receive N+T+F (oral neratinib 240 mg/day, i.v. trastuzumab 8 mg/kg initially followed by 6 mg/kg every 3 weeks, and i.m. fulvestrant 500 mg on days 1&15 of month 1, then on day 1 every 4 weeks). Loperamide prophylaxis was mandatory during the first 2 treatment cycles. There was no restriction on the number of prior lines of systemic treatment for MBC. Efficacy endpoints: confirmed objective response rate and clinical benefit rate (RECIST v1.1); duration of response; progression-free survival. Results: As of 22-May-2020, 46 patients were enrolled in the N+T+F cohort and received at least 1 dose of study medication (safety population). 14 unique HER2 allelic variants were identified: 8 kinase domain missense; 1 extracellular domain missense; 2 transmembrane domain missense; 2 exon-20 insertion; 1 exon-19 deletion. The most common HER2 mutant variant was L755S (n=15, 33%) Median number of prior systemic regimens for metastatic disease was 4 (range 0-10); 34 (74%) patients had received prior fulvestrant, and 31 (67%) patients had received prior cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor therapy. 16 (35%) patients had ductal histology, 29 (63%) had lobular carcinoma, and 1 (2%) had mixed ductal and lobular carcinoma. At this time, 30/46 patients had RECIST measurable disease and are efficacy evaluable (ongoing patients who did not have the opportunity for their first post-baseline tumor assessment were excluded); clinical activity - see Table. Diarrhea was the most commonly reported adverse event (80% any grade) with 15 (33%) patients reporting grade 3 diarrhea (no grade 4 diarrhea). 10 patients (22%) had a neratinib dose reduction due to diarrhea but no patients discontinued treatment due to diarrhea. Conclusions: The combination of N+T+F demonstrated encouraging clinical activity in heavily pre-treated HER2-mutant, HR+, HER2-non-amplified MBC, including patients who had previously received either fulvestrant and/or CDK4/6 inhibitor-based therapies. While the rate of grade 3 diarrhea was higher than that observed with single-agent neratinib in SUMMIT, this was manageable through loperamide prophylaxis, and no patients discontinued study treatment due to diarrhea. SUMMIT has recently been amended to evaluate N+T+F, T+F and F (1:1:1 randomization) and continues to enroll patients. RECIST measurable and efficacy evaluable patients (n=30)Confirmed objective response,a n (%)12 (40)CR0PR12ORR, % (95% CI)40 (23-59)Best overall response, n (%)18 (60)CR0PR18Best overall response rate, % (95% CI)60 (41-77)Medianb DOR, months (95% CI)8.4 (4.1-NE)Clinical benefit,c n (%)14 (47)CR or PR12SD ≥24 weeks2CBR, % (95% CI)47 (28-66)Medianb PFS, months (95% CI)8.3 (4.2-12.5)aORR is defined as either a CR or a PR that is confirmed no less than 4 weeks after the criteria for response are initially met; bKaplan-Meier analysis; cCBR is defined as confirmed CR or PR or SD for ≥24 weeks; CR, complete response; CBR, clinical benefit rate; DOR, duration of response; NE, not estimable; ORR, objective response rate; PFS, progression-free survival; PR, partial response; SD, stable disease. Citation Format: Komal Jhaveri, Cristina Saura, Angel Guerrero-Zotano, Iben Spanggaard, François-Clement Bidard, Jonathan W Goldman, José A García-Sáenz, Andrés Cervantes, Valentina Boni, John Crown, Adam Brufsky, Sherene Loi, Barbara Haley, Ingrid A Mayer, Stephen Chia, Janice Lu, James Waisman, Noa Efrat Ben-Baruch, Mark E Burkard, Jennifer M Suga, Lucía González-Cortijo, Bruno Perrucci, Feng Xu, Sofia Wong, Jie Zhang, Lisa D Eli, Alshad S Lalani, Hans Wildiers. Latest findings from the breast cancer cohort in SUMMIT - a phase 2 ‘basket’ trial of neratinib + trastuzumab + fulvestrant for HER2-mutant, hormone receptor-positive, metastatic breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD1-05.

Background: Several studies suggest clinical utility of serial circulating tumor cell (CTC) enumeration as a means of assessing response status in metastatic breast cancer (MBC). The aim of this study is to conduct a comprehensive pooled analysis comprising globally available data to further define and explore the role of CTC enumeration as a tool for early treatment monitoring in patients with MBC with a focus on the predictive power in different breast cancer subtypes and clinical settings. Methods: In a global effort, peer-reviewed published studies with data on repeated CTC assessments (CellSearch® technology; Menarini Silicon Biosystems; Bologna, Italy) in MBC patients were screened and investigators were asked to provide individual patient data for this pooled analysis. 2761 cases from 32 data sets with data on both baseline and one follow up CTC assessments were included in the analysis (median time interval between the two CTC assessments 35 days). Data were analyzed using log rank tests and Cox regressions to evaluate the association between serial CTC enumeration results and overall survival (OS) in the full patient cohort and defined subgroups. Results: 588 (21.3%) patients had no CTCs at both time points (neg/neg), 236 (8.5%) patients were CTC negative at baseline and CTC positive at follow up (neg/pos), 712 (25.8%) patients converted from CTC positive at baseline to CTC negative (pos/neg), and 1225 (44.4%) patients had at least one CTC at both time points (pos/pos). Log rank tests showed significant differences in OS between these four CTC change groups (p < 0.0001 for all pairwise comparisons except for the comparison between neg/pos and pos/neg, p = 0.015). Median OS for the neg/neg, neg/pos, pos/neg and pos/pos group was 45.6, 26.1, 34.6, and 17.6 months, respectively. Hazard ratios (HR) (reference group neg/neg) were 1.38 (95% CI 1.16 - 1.64) for the pos/neg group, 1.78 (95% CI 1.43 - 2.22) for the neg/pos group, and 3.06 (95% CI 2.63 - 3.56) for the pos/pos group. Results were similar if a cutoff of 5 CTCs was used for CTC positivity (pos/neg group: HR 1.43, 95% CI 1.25 - 1.63; neg/pos group: HR 2.39, 95% CI 1.91 - 2.99; pos/pos group: HR 3.54, 95% CI 3.12 - 4.02). In total, 2586 patients could be assigned to different tumor subtypes based on known hormone receptor (ER) and HER2 status of the primary tumor: 1513 (58.5%) patients had a luminal-like tumor (ER positive, HER2 negative), 682 (26.4%) patients had a HER2-positive tumor, and 391 (15.1%) patients had a triple-negative tumor. In patients with luminal-like tumors, the hazard ratios were 1.67 (95% CI 1.29 - 2.17), 2.01 (95% CI 1.45 - 2.77), and 3.87 (95% CI 3.09 - 4.83) for the pos/neg, neg/pos, and pos/pos group, respectively. In patients with HER2-positive tumors, the neg/pos group (HR 1.68, 95% CI 1.12 - 2.53) and the pos/pos group (HR 2.11, 95% CI 1.58 - 2.83) showed significantly worse OS compared to the neg/neg group, while in triple-negative patients, the pos/pos group had a significantly shorter OS compared to the neg/neg group (HR 2.99, 95% CI 2.11 - 4.24). The results will be up-dated by inclusion of additional large data sets (CALGB 40502, CALGB 40503, COMET, SWOG S0500, TBCRC 001) for the analysis to be presented at SABCS 2020. Conclusion: This large pooled analysis confirms that at a median of 35 days after treatment initiation, follow-up CTC assessments strongly predict overall survival. These results suggest potential clinical utility of CTC monitoring as early response marker in MBC, especially in luminal-like tumors. Citation Format: Wolfgang J Janni, Tracy C. Yab, Daniel F. Hayes, Massimo Cristofanilli, Francois-Clement Bidard, Michail Ignatiadis, Meredith M. Regan, Catherine Alix-Panabières, William E. Barlow, Carlos Caldas, Lisa A. Carey, Luc Dirix, Tanja Fehm, Jose A. Garcia-Saenz, Paola Gazzaniga, Daniele Generali, Lorenzo Gerratana, Rafael Gisbert-Criado, William Jacot, Zefei Jiang, Evi Lianidou, Mark J.M. Magbanua, Luis Manso, Dimitrios Mavroudis, Volkmar Müller, Elisabetta Munzone, Klaus Pantel, Jean-Yves Pierga, Brigitte Rack, Sabine Riethdorf, Hope S. Rugo, Kostandinos Sideras, Stefan Sleijfer, Jeffrey Smerage, Justin Stebbing, Leon W.M.M. Terstappen, José Vidal-Martínez, Rita Zamarchi, Karthik Giridhar, Thomas W.P. Friedl, Minetta C. Liu. Clinical utility of repeated circulating tumor cell (CTC) enumeration as early treatment monitoring tool in metastatic breast cancer (MBC) - a global pooled analysis with individual patient data [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr GS4-08.

Genome-wide analysis identifies 32 loci associated with breast cancer susceptibility, accounting for estrogen receptor, progesterone receptor and human epidermal growth factor receptor 2 status and tumor grade. Breast cancer susceptibility variants frequently show heterogeneity in associations by tumor subtype(1-3). To identify novel loci, we performed a genome-wide association study including 133,384 breast cancer cases and 113,789 controls, plus 18,908 BRCA1 mutation carriers (9,414 with breast cancer) of European ancestry, using both standard and novel methodologies that account for underlying tumor heterogeneity by estrogen receptor, progesterone receptor and human epidermal growth factor receptor 2 status and tumor grade. We identified 32 novel susceptibility loci (P < 5.0 x 10(-8)), 15 of which showed evidence for associations with at least one tumor feature (false discovery rate < 0.05). Five loci showed associations (P < 0.05) in opposite directions between luminal and non-luminal subtypes. In silico analyses showed that these five loci contained cell-specific enhancers that differed between normal luminal and basal mammary cells. The genetic correlations between five intrinsic-like subtypes ranged from 0.35 to 0.80. The proportion of genome-wide chip heritability explained by all known susceptibility loci was 54.2% for luminal A-like disease and 37.6% for triple-negative disease. The odds ratios of polygenic risk scores, which included 330 variants, for the highest 1% of quantiles compared with middle quantiles were 5.63 and 3.02 for luminal A-like and triple-negative disease, respectively. These findings provide an improved understanding of genetic predisposition to breast cancer subtypes and will inform the development of subtype-specific polygenic risk scores.

PURPOSE Patients with pretreated estrogen receptor (ER)–positive/human epidermal growth factor receptor 2 (HER2)–negative advanced breast cancer have poor prognosis. Elacestrant is a novel, oral selective ER degrader that demonstrated activity in early studies. METHODS This randomized, open-label, phase III trial enrolled patients with ER-positive/HER2-negative advanced breast cancer who had one-two lines of endocrine therapy, required pretreatment with a cyclin-dependent kinase 4/6 inhibitor, and ≤ 1 chemotherapy. Patients were randomly assigned to elacestrant 400 mg orally once daily or standard-of-care (SOC) endocrine monotherapy. Primary end points were progression-free survival (PFS) by blinded independent central review in all patients and patients with detectable ESR1 mutations. RESULTS Patients were randomly assigned to elacestrant (n = 239) or SOC (n = 238). ESR1 mutation was detected in 47.8% of patients, and 43.4% received two prior endocrine therapies. PFS was prolonged in all patients (hazard ratio = 0.70; 95% CI, 0.55 to 0.88; P = .002) and patients with ESR1 mutation (hazard ratio = 0.55; 95% CI, 0.39 to 0.77; P = .0005). Treatment-related grade 3/4 adverse events occurred in 7.2% receiving elacestrant and 3.1% receiving SOC. Treatment-related adverse events leading to treatment discontinuations were 3.4% in the elacestrant arm versus 0.9% in SOC. Nausea of any grade occurred in 35.0% receiving elacestrant and 18.8% receiving SOC (grade 3/4, 2.5% and 0.9%, respectively). CONCLUSION Elacestrant is the first oral selective ER degrader demonstrating a significant PFS improvement versus SOC both in the overall population and in patients with ESR1 mutations with manageable safety in a phase III trial for patients with ER-positive/HER2-negative advanced breast cancer.

Background Whether there are lifetime points of greater sensitivity to the deleterious effects of alcohol intake on the breasts remains inconclusive. Objective To compare the influence of distinctive trajectories of alcohol consumption throughout a woman's life on development of breast cancer (BC). Methods 1278 confirmed invasive BC cases and matched (by age and residence) controls from the Epi-GEICAM study (Spain) were used. The novel group-based trajectory modelling was used to identify different alcohol consumption trajectories throughout women's lifetime. Results Four alcohol trajectories were identified. The first comprised women (45%) with low alcohol consumption (= 15 g/day), never having a low alcohol consumption. Comparing with the first trajectory, the fourth doubled BC risk (OR 2.19; 95% CI 1.27, 3.77), followed by the third (OR 1.44; 0.96, 2.16) and ultimately by the second trajectory (OR 1.17; 0.86, 1.58). The magnitude of BC risk was greater in postmenopausal women, especially in those with underweight or normal weight. When alcohol consumption was independently examined at each life stage, >= 15 g/day of alcohol consumption in adolescence was strongly associated with BC risk followed by consumption in adulthood. Conclusions The greater the alcohol consumption accumulated throughout life, the greater the risk of BC, especially in postmenopausal women. Alcohol consumption during adolescence may particularly influence BC risk., This study was funded by the Fundacion Cientifica Asociacion Espanola Contra el Cancer (AECC) (Scientific Foundation of the Spanish Association against Cancer 2006 & 2016) (Marina Pollan), Sociedad Espanola de Oncologia Medica (SEOM) (Spanish Society of Medical Oncology) (Miguel Martin), Scholarship 'Contrato de atraccion de talento' from Community of Madrid (Carolina Donat-Vargas), Fundacion Cerveza y Salud 2005 (Beer and Health Foundation 2005) (Miguel Martin) and Federacion de Asociaciones de Mujeres con Cancer de Mama (FECMA) (Spanish Federation of Associations of Women with Breast Cancer) (Miguel Martin, Marina Pollan).

© 2021 by the authors., Alternative splicing is an essential biological process, which increases the diversity and complexity of the human transcriptome. In our study, 304 splicing pathway-related genes were evaluated in tumors from breast cancer patients (TCGA dataset). A high number of alterations were detected, including mutations and copy number alterations (CNAs), although mutations were less frequently present compared with CNAs. In the four molecular subtypes, 14 common splice genes showed high level amplification in >5% of patients. Certain genes were only amplified in specific breast cancer subtypes. Most altered genes in each molecular subtype clustered to a few chromosomal regions. In the Luminal subtype, amplifications of LSM1, CLNS1A, and ILF2 showed a strong significant association with prognosis. An even more robust association with OS and RFS was observed when expression of these three genes was combined. Inhibition of LSM1, CLNS1A, and ILF2, using siRNA in MCF7 and T47D cells, showed a decrease in cell proliferation. The mRNA expression of these genes was reduced by treatment with BET inhibitors, a family of epigenetic modulators. We map the presence of splicing-related genes in breast cancer, describing three novel genes, LSM1, CLNS1A, and ILF2, that have an oncogenic role and can be modulated with BET inhibitors., A.O.’s lab is supported by the Instituto de Salud Carlos III (ISCIII, PI19/00808); ACEPAIN; CRIS Cancer Foundation and Diputación de Albacete. This research is also supported by PI18/01020 from the Instituto de Salud Carlos III and co-financed by the European Development Regional Fund (FEDER) “A way to achieve Europe” (ERDF); N.L. MDM was supported by the Spanish Ministry of Education (FPU grant; Ref.: FPU18/01319). B.G. was financed by the 2018-2.1.17-TETKR-00001, 2020-1.1.6-JÖVO-2021-00013, and 2018-1.3.1-VKE-2018-00032 grants and by the Higher ˝ Education Institutional Excellence Programme (2020-4.1.1.-TKP2020) of the Ministry for Innovation and Technology in Hungary.

Purpose: This phase II study investigated daily or weekly sapanisertib (a selective dual inhibitor of mTOR complexes 1 and 2) in combination with fulvestrant. Patients and Methods: Postmenopausal women with estrogen receptor–positive (ER+)/HER2-negative (HER2−) advanced or metastatic breast cancer following progression during/after aromatase inhibitor treatment were randomized to receive fulvestrant 500 mg (28-day treatment cycles), fulvestrant plus sapanisertib 4 mg daily, or fulvestrant plus sapanisertib 30 mg weekly, until progressive disease, unacceptable toxicity, consent withdrawal, or study completion. Results: Among 141 enrolled patients, baseline characteristics were balanced among treatment arms, including prior cyclin-dependent kinase-4/6 (CDK4/6) inhibitor treatment in 33% to 35% of patients. Median progression-free survival (PFS; primary endpoint) was 3.5 months in the single-agent fulvestrant arm, compared with 7.2 months for fulvestrant plus sapanisertib daily [HR, 0.77; 95% confidence interval (CI), 0.47–1.26] and 5.6 months for fulvestrant plus sapanisertib weekly (HR, 0.88; 95% CI, 0.53–1.45). The greatest PFS benefits were seen in patients who had previously received CDK4/6 inhibitors. The most common adverse events were nausea, vomiting, and hyperglycemia, all occurring more frequently in the combination therapy arms. Treatment discontinuation due to adverse events occurred more frequently in the two combination therapy arms than with single-agent fulvestrant (32% and 36% vs. 4%, respectively). Conclusions: Fulvestrant plus sapanisertib daily/weekly resulted in numerically longer PFS in patients with ER+/HER2− advanced or metastatic breast cancer, compared with single-agent fulvestrant. The combination was associated with increased toxicity. Further development of sapanisertib using these dosing schedules in this setting is not supported by these data.

Introduction: Breast cancer is the first cause of cancer death in women. The triple-negative subtype is associated with aggressive behavior and poor prognosis. Chemotherapy is the main therapeutic option available for these patients, but it is usually associated with short overall survival. Case Presentation: We report the case of a patient diagnosed with metastatic triple-negative breast cancer with an impressive long-lasting tumor response and long-term survival after pembrolizumab monotherapy. Conclusion: Immunotherapy is emerging as a promising treatment for some breast cancer patients. Nevertheless, monotherapy studies have shown a very limited activity. Nowadays, there is no good predictor biomarker. Further investigations are needed to identify the subgroup of patients who can benefit from checkpoint inhibitor treatment.

Introduction An increase in the number of cancer cases is expected in the near future. Breast cancer (BC) mortality rates increase with age even when adjusted for other variables. Here we analyzed BC disease-free survival (BCDFS) and BC specific survival (BCSS) in the El Alamo III BC registry of GEICAM Spanish Breast Cancer Group. Materials and methods El Alamo III is a retrospective registry of BC patients diagnosed between 1998 and 2001. Patients with stage I-III invasive BC of age groups 55-64 years (y), 70-74 years and >= 75 years were included. Patients and tumors characteristics, treatments and recurrences and deaths were analyzed. Results 4343 patients were included within the following age intervals: 2288 (55-64 years), 960 (70-74 years), and 1095 (>= 75 years). Older patients (>= 70 years) were diagnosed with more advanced tumors (stage III) than younger patients (21.5% versus 13.4%, p < 0.0001). Mastectomies were performed more on older patients and they received less chemotherapy than younger patients (66.6% versus 43.1%, p < 0.00001 and 30.8% versus 71.6%, p < 0.0001, respectively). With a median follow-up of 5.9 years, 17.7% patients had BCDFS events in the younger group and 19.8% in the older group (p < 0.0001). A decrease in BCSS was also observed in older patients, either when analyzing patients >= 70y (p < 0.0001) and when differentiating by the two older groups (p < 0.0001). Conclusions Our study suggests that older BC patients have worse outcomes what can be a consequence of receiving inadequate adjuvant treatments. Specific trials for these patients are warranted to allow us to treat them with the same scientific rigor than younger patients.

Eribulin is active and safe in heavily pre-treated metastatic breast cancer patients. Few safety data have been published in third line. We aimed to report the specific safety profile on third line beyond taxanes and anthracyclines in advanced breast cancer (ABC). A multicenter phase II, prospective study was conducted in anthracyclines and taxanes pre-treated HER2-negative ABC, programmed to receive eribulin as third-line chemotherapy. Adverse events (AEs) were assessed and classified according to CTCAE. In addition, efficacy, in terms of overall survival (OS) and progression-free survival (PFS), and the dynamics of circulating tumor cells (CTCs) during treatment were assessed. 59 patients fulfilled the criteria. All but one showed AEs with a cumulative number of 598 AEs. The most frequent grade 3/4 drug-related AEs were neutropenia (1.7%), febrile neutropenia (0.5%), leukopenia (0.5%), alopecia (0.5%), asthenia (0.3%), elevated gamma glutamyl transferase levels (0.2%), and respiratory tract infection (0.2%). Median PFS was 4 months (95% CI 3.1-5.9) and median OS was 13.6 months (11.8-not reached). The mean number of CTCs in peripheral blood was significantly reduced from baseline to cycle 2 (16.8 vs 5.4 CTCs; P < 0.001). Median OS was significantly longer in

TPS1109 Background: Endocrine therapy (ET) + CDK4/6i is standard of care for HR+, HER2− ABC; however, CDK4/6i resistance, in which the phosphatidylinositol-3-kinase (PI3K) pathway has a key role, remains challenging. Progression-free survival (PFS) for ≥ 2nd-line ET monotherapy post CDK4/6i is poor; prognosis may be worse in patients with a PI3KCA mutation. ALP (PI3K-α selective inhibitor and degrader) + FUL is approved by the European Medicines Agency (EMA) for HR+, HER2–, PIK3CA-mutated ABC after ET monotherapy. Outside the EMA, ALP + FUL approval includes post-CDK4/6i use. ALP + FUL has shown clinical activity and consistent safety in a small subpopulation in SOLAR-1 with prior CDK4/6i treatment (n = 9) and in BYLieve Cohort A (CDK4/6i + AI as immediate prior treatment; n = 121). The EPIK-B5 study aims to confirm the efficacy and safety of ALP + FUL in a larger population with HR+, HER2–, PIK3CA-mutated ABC with prior CDK4/6i + AI treatment. Methods: EPIK-B5 is a Phase III, randomized (1:1), double-blind, placebo-controlled study assessing the efficacy and safety of ALP (300 mg/d orally starting Cycle 1 Day 1 [C1D1]) + FUL (500 mg intramuscularly on C1D1 and C1D15, and D1 of subsequent cycles) in patients (N ≈ 234) with HR+, HER2–, PIK3CA-mutated ABC progressing on/after CDK4/6i + AI. Patients randomized to placebo + FUL can cross over to ALP + FUL after progression. Randomization is stratified by presence of lung and/or liver metastasis and prior CDK4/6i setting. Adult men or postmenopausal women with confirmed HR+, HER2–, PIK3CA-mutated ABC and ≥ 1 measurable lesion are eligible. The primary endpoint is PFS per blinded independent review committee assessment. Secondary endpoints include overall survival, overall response and clinical benefit rates, duration of and time to response, PFS by PIK3CA-mutation status in circulating tumor DNA, PFS on next-line treatment, time to definitive deterioration of ECOG status, quality of life (QoL), and safety and tolerability. Exploratory endpoints include biomarker analyses, additional QoL endpoints, and time to subsequent chemotherapy. Recruitment is ongoing, with enrollment planned over 2 years in 18 countries; completion of primary data collection is anticipated in 2026. Clinical trial information: NCT05038735; EUDRACT2021-001966-39.

BackgroundWe examined the prognostic significance of circulating tumor cell (CTC) dynamics during treatment in metastatic breast cancer (MBC) patients receiving first-line chemotherapy.MethodsSerial CTC data from 469 patients (2202 samples) were used to build a novel latent mixture model to identify groups with similar CTC trajectory (tCTC) patterns during the course of treatment. Cox regression was used to estimate hazard ratios for progression-free survival (PFS) and overall survival (OS) in groups based on baseline CTCs, combined CTC status at baseline to the end of cycle 1, and tCTC. Akaike information criterion was used to select the model that best predicted PFS and OS.ResultsLatent mixture modeling revealed 4 distinct tCTC patterns: undetectable CTCs (56.9% ), low (23.7%), intermediate (14.5%), or high (4.9%). Patients with low, intermediate, and high tCTC patterns had statistically significant inferior PFS and OS compared with those with undetectable CTCs (P < .001). Akaike Information Criterion indicated that the tCTC model best predicted PFS and OS compared with baseline CTCs and combined CTC status at baseline to the end of cycle 1 models. Validation studies in an independent cohort of 1856 MBC patients confirmed these findings. Further validation using only a single pretreatment CTC measurement confirmed prognostic performance of the tCTC model.ConclusionsWe identified 4 novel prognostic groups in MBC based on similarities in tCTC patterns during chemotherapy. Prognostic groups included patients with very poor outcome (intermediate + high CTCs, 19.4%) who could benefit from more effective treatment. Our novel prognostic classification approach may be used for fine-tuning of CTC-based risk stratification strategies to guide future prospective clinical trials in MBC.

Background Given the high heterogeneity among breast tumors, associations between common germline genetic variants and survival that may exist within specific subgroups could go undetected in an unstratified set of breast cancer patients. Methods We performed genome-wide association analyses within 15 subgroups of breast cancer patients based on prognostic factors, including hormone receptors, tumor grade, age, and type of systemic treatment. Analyses were based on 91,686 female patients of European ancestry from the Breast Cancer Association Consortium, including 7531 breast cancer-specific deaths over a median follow-up of 8.1 years. Cox regression was used to assess associations of common germline variants with 15-year and 5-year breast cancer-specific survival. We assessed the probability of these associations being true positives via the Bayesian false discovery probability (BFDP Results Evidence of associations with breast cancer-specific survival was observed in three patient subgroups, with variant rs5934618 in patients with grade 3 tumors (15-year-hazard ratio (HR) [95% confidence interval (CI)] 1.32 [1.20, 1.45], P = 1.4E−08, BFDP = 0.01, per G allele); variant rs4679741 in patients with ER-positive tumors treated with endocrine therapy (15-year-HR [95% CI] 1.18 [1.11, 1.26], P = 1.6E−07, BFDP = 0.09, per G allele); variants rs1106333 (15-year-HR [95% CI] 1.68 [1.39,2.03], P = 5.6E−08, BFDP = 0.12, per A allele) and rs78754389 (5-year-HR [95% CI] 1.79 [1.46,2.20], P = 1.7E−08, BFDP = 0.07, per A allele), in patients with ER-negative tumors treated with chemotherapy. Conclusions We found evidence of four loci associated with breast cancer-specific survival within three patient subgroups. There was limited evidence for the existence of associations in other patient subgroups. However, the power for many subgroups is limited due to the low number of events. Even so, our results suggest that the impact of common germline genetic variants on breast cancer-specific survival might be limited.

Author(s): Coignard, Juliette; Lush, Michael; Beesley, Jonathan; O'Mara, Tracy A; Dennis, Joe; Tyrer, Jonathan P; Barnes, Daniel R; McGuffog, Lesley; Leslie, Goska; Bolla, Manjeet K; Adank, Muriel A; Agata, Simona; Ahearn, Thomas; Aittomaki, Kristiina; Andrulis, Irene L; Anton-Culver, Hoda; Arndt, Volker; Arnold, Norbert; Aronson, Kristan J; Arun, Banu K; Augustinsson, Annelie; Azzollini, Jacopo; Barrowdale, Daniel; Baynes, Caroline; Becher, Heko; Bermisheva, Marina; Bernstein, Leslie; Bialkowska, Katarzyna; Blomqvist, Carl; Bojesen, Stig E; Bonanni, Bernardo; Borg, Ake; Brauch, Hiltrud; Brenner, Hermann; Burwinkel, Barbara; Buys, Saundra S; Caldes, Trinidad; Caligo, Maria A; Campa, Daniele; Carter, Brian D; Castelao, Jose E; Chang-Claude, Jenny; Chanock, Stephen J; Chung, Wendy K; Claes, Kathleen BM; Clarke, Christine L; GEMO Study Collaborators; EMBRACE Collaborators; Collee, J Margriet; Conroy, Don M; Czene, Kamila; Daly, Mary B; Devilee, Peter; Diez, Orland; Ding, Yuan Chun; Domchek, Susan M; Dork, Thilo; Dos-Santos-Silva, Isabel; Dunning, Alison M; Dwek, Miriam; Eccles, Diana M; Eliassen, A Heather; Engel, Christoph; Eriksson, Mikael; Evans, D Gareth; Fasching, Peter A; Flyger, Henrik; Fostira, Florentia; Friedman, Eitan; Fritschi, Lin; Frost, Debra; Gago-Dominguez, Manuela; Gapstur, Susan M; Garber, Judy; Garcia-Barberan, Vanesa; Garcia-Closas, Montserrat; Garcia-Saenz, Jose A; Gaudet, Mia M; Gayther, Simon A; Gehrig, Andrea; Georgoulias, Vassilios; Giles, Graham G; Godwin, Andrew K; Goldberg, Mark S; Goldgar, David E | Abstract: A Correction to this paper has been published: https://doi.org/10.1038/s41467-021-23162-4.

Breast cancer metastasis accounts for most of the deaths from breast cancer. Identification of germline variants associated with survival in aggressive types of breast cancer may inform understanding of breast cancer progression and assist treatment. In this analysis, we studied the associations between germline variants and breast cancer survival for patients with distant metastases at primary breast cancer diagnosis. We used data from the Breast Cancer Association Consortium (BCAC) including 1062 women of European ancestry with metastatic breast cancer, 606 of whom died of breast cancer. We identified two germline variants on chromosome 1, rs138569520 and rs146023652, significantly associated with breast cancer-specific survival (P = 3.19 × 10−8 and 4.42 × 10−8). In silico analysis suggested a potential regulatory effect of the variants on the nearby target genes SDE2 and H3F3A. However, the variants showed no evidence of association in a smaller replication dataset. The validation dataset was obtained from the SNPs to Risk of Metastasis (StoRM) study and included 293 patients with metastatic primary breast cancer at diagnosis. Ultimately, larger replication studies are needed to confirm the identified associations.

BACKGROUND: Palbociclib plus endocrine therapy (ET) is the standard treatment for hormone receptor-positive and human epidermal growth factor receptor 2-negative, metastatic breast cancer (MBC). However, its efficacy has not been compared with that of chemotherapy in a phase III trial. PATIENTS AND METHODS: PEARL is a multicentre, phase III randomised study in which patients with aromatase inhibitors (AIs)-resistant MBC were included in two consecutive cohorts. In cohort 1 (C1), patients were randomised 1:1 to palbociclib plus exemestane or capecitabine. On discovering new evidence about oestrogen receptor-1 (ESR1) mutations inducing resistance to AIs, the trial was amended to include cohort 2 (C2), in which patients were randomised 1:1 between palbociclib plus fulvestrant and capecitabine. The stratification criteria were disease site, prior sensitivity to ET, prior chemotherapy for MBC, and country of origin. Co-primary endpoints were progression-free survival (PFS) in C2 and in wild-type ESR1 patients (C1+C2). ESR1 hotspot mutations were analysed in baseline circulating tumour DNA. RESULTS: From March-2014 to July-2018, 296 and 305 patients were included in C1 and C2, respectively. Palbociclib plus ET was not superior to capecitabine in both C2 (median PFS: 7.5 vs. 10.0 months; adjusted hazard ratio [aHR]: 1.13; 95% confidence Interval [CI]: 0.85-1.50) and wild-type ESR1 patients (median PFS: 8.0 vs. 10.6 months; aHR: 1.11; 95% CI: 0.87-1.41). The most frequent grade 3-4 toxicities with palbociclib plus exemestane, palbociclib plus fulvestrant, and capecitabine were neutropenia (57.4%, 55.7% and 5.5%), hand/foot syndrome (0%, 0% and 23.5%), and diarrhoea (1.3%, 1.3% and 7.6%). Palbociclib plus ET offered better quality of life (aHR for time to deterioration of global health status: 0.67; 95% CI: 0.53-0.85). CONCLUSIONS: There was no statistical superiority of palbociclib plus ET over capecitabine with respect to PFS in MBC patients resistant to AIs. Palbociclib plus ET showed a better safety profile and improved quality of life.