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Poly-ADP ribose polymerase (PARP) inhibitors (PARPi) are active in patients with germline BRCA1/2 (gBRCA1/2)-mutated breast cancer, accounting for 5% to 10% of all breast cancers. Another 5% to 10% harbor somatic BRCA1/2 (sBRCA1/2) mutations or mutations in non-BRCA1/2, homologous recombination repair (HRR) genes but until recently, there were no data for the use of PARPi in these patients. This study examines the use of olaparib in patients with metastatic breast cancer harboring sBRCA1/2 or germline or somatic non-BRCA1/2, HRR mutations and demonstrates potential activity of PARPi in this setting.In this retrospective, single institution study, patients who were treated with off-label, off-protocol olaparib for metastatic breast cancer harboring sBRCA1/2 or germline or somatic non-BRCA1/2, HRR mutations were identified. The primary aim was to describe these patients' demographics, tumor characteristics, mutations, safety and tolerability, response rates, progression free survival, PARPi-associated survival and subsequent treatment.Seven patients were treated off-label, off-trial with olaparib for sBRCA1/2-mutated cancers (n = 4) or non-BRCA1/2, HRR-mutated cancers (n = 3). All patients with sBRCA1/2-mutated cancers responded to PARP inhibition; patients with non-BRCA1/2, HRR-mutated cancers did not respond. The median progression free survival in patients with a sBRCA1/2 mutation was 6.5 months (range 5-9 months) vs. 3 months (range 2-4 months) in patients with non-BRCA1/2, HRR mutations.This single institution experience adds to recent larger reports confirming evidence for PARPi therapy in patients with metastatic breast cancer harboring sBRCA1/2 mutations. No activity was observed in patients with either germline or somatic non-BRCA1/2, HRR-mutated cancers.

Purpose Expanded access programs (EAPs) allow patients with cancer who have unmet clinical needs to obtain access to pre-authorisation treatments. There is no standardised process or registry for implementing these programs nationally and real world data on their impact is lacking. We evaluated their prevalence and impact in a cancer centre.Methods Data relating to adult cancer patients treated via EAPs from 2011 to 2021 in three Cork university hospitals was collated. Descriptive statistics were employed to get an overview of the impact these programs currently have on cancer care provision.Results We identified 193 patients who accessed EAPs during the study period, availing of 33 separate drugs for a total of 50 different cancer indications. The prevalence of EAP usage was shown to have been trending upwards in recent years with a total of 189 programs being accessed throughout the period. Drugs provided were from a number of different anti-cancer drug classes, particularly targeted therapies (n = 18) and immune checkpoint inhibitors (n = 17). Cancers from a wide range of both solid and liquid tumour types were identified as having been treated with EAP drugs and patients treated were from across a broad spectrum of ages (26–82, SD:11.99).Conclusion EAPs have an increasing role in access to novel cancer therapies in our community and by extension nationally. Equity of EAP access would be facilitated by a national registry of available agents which we have now established. Assessment of their benefits and toxicities would be enhanced by the requirement for a real world data base as a condition of EAP approval.

Supplementary Data from Entinostat Decreases Immune Suppression to Promote Antitumor Responses in a HER2+ Breast Tumor Microenvironment

The supplemental tables include: antibodies used for flow cytometry; gene expression of genes involved in innate and adaptive immunity from whole tumors isolated from neu-N mice.

This file contains supplemental figures that includes: FACS gating strategies; QC plots for NanoString cell typing; survival and tumor growth of neu-N mice receiving ENT and ICIs without ï�¡-HER2; circulating MDSCs and absolute numbers of G-MDSCs infiltrating neu-N and Panc02 tumors; G-MDSCs quantified using flow cytometry from neu-N tumors or from hepatic Panc02 metastases; MDSC functional markers by flow cytometry and expression of PD-L1 on G-MDSCs; patterns of myeloid cell functional markers on gene expression profiling; qPCR validation of NanoString, and T cell proliferation and IFNï�§ï€ production within the TME; western blots depicting protein expression levels of STAT3 and phospho-STAT3 and representative proteins from NanoString pathways; the exhaustion state of CD8+ T cells.

Immune-checkpoint inhibition (ICI) has revolutionized treatment in cancers that are naturally immunogenic by enabling infiltration of T cells into the tumor microenvironment (TME) and promoting cytotoxic signaling pathways. Tumors possessing complex immunosuppressive TMEs such as breast and pancreatic cancers present unique therapeutic obstacles as response rates to ICI remain low. Such tumors often recruit myeloid-derived suppressor cells (MDSCs), whose functioning prohibits both T-cell activation and infiltration. We attempted to sensitize these tumors to ICI using epigenetic modulation to target MDSC trafficking and function to foster a less immunosuppressive TME. We showed that combining a histone deacetylase inhibitor, entinostat (ENT), with anti–PD-1, anti–CTLA-4, or both significantly improved tumor-free survival in both the HER2/neu transgenic breast cancer and the Panc02 metastatic pancreatic cancer mouse models. Using flow cytometry, gene-expression profiling, and ex vivo functional assays, we characterized populations of tumor-infiltrating lymphocytes (TILs) and MDSCs, as well as their functional capabilities. We showed that addition of ENT to checkpoint inhibition led to significantly decreased suppression by granulocytic MDSCs in the TME of both tumor types. We also demonstrated an increase in activated granzyme-B–producing CD8+ T effector cells in mice treated with combination therapy. Gene-expression profiling of both MDSCs and TILs identified significant changes in immune-related pathways. In summary, addition of ENT to ICI significantly altered infiltration and function of innate immune cells, allowing for a more robust adaptive immune response. These findings provide a rationale for combination therapy in patients with immune-resistant tumors, including breast and pancreatic cancers.

Supplementary figure legends (S1-S11) clean AND supplementary table legends (1-2) clean.

Exploratory analysis comparing weight loss across various clinical subgroups.

Global and promoter CpG island demethylation in available paired pre- and post-treatment (8 weeks) hormone-resistant and triple-negative tumor biopsies.

Supplemental figure S4

Supplemental Figure 1: CONSORT Diagram

Purpose:Epigenetic modulators improve immune checkpoint inhibitor (ICI) efficacy and increase CD8+ effector:FoxP3+ regulatory T cell ratios in preclinical models. We conducted a multicenter phase I clinical trial combining the histone deacetylase inhibitor entinostat with nivolumab ± ipilimumab in advanced solid tumors.Patients and Methods:Patients received an entinostat run-in (5 mg, weekly × 2) prior to the addition of ICIs. Dose escalation followed a modified 3+3 design [dose level (DL)1/2: entinostat + nivolumab; DL 3/4: entinostat + nivolumab + ipilimumab]. Blood and tissue samples were collected at baseline, after entinostat run-in, and after 8 weeks of combination therapy. Primary endpoints included safety and tolerability, and the recommended phase II dose (RP2D). Secondary endpoints included antitumor activity and change in tumor CD8/FoxP3 ratio pre- and post-therapy.Results:Thirty-three patients were treated across four dose levels. Treatment-related adverse events (AE) included fatigue (65%), nausea (41%), anemia (38%), diarrhea (26%), and anorexia (26%). Grade 3/4 AEs included fatigue (n = 7, 21%), anemia (n = 9, 27%), and neutropenia (n = 4, 12%). The RP2D was 3 mg entinostat weekly, 3 mg/kg every 2 weeks nivolumab, and 1 mg/kg every 6 weeks ipilimumab (max four doses). The objective response rate by RECIST 1.1 was 16%, including a complete response in triple-negative breast cancer. A statistically significant increase in CD8/FoxP3 ratio was seen following the addition of ICIs to entinostat, but not post-entinostat alone.Conclusions:The combination of entinostat with nivolumab ± ipilimumab was safe and tolerable with expected rates of immune-related AEs. Preliminary evidence of both clinical efficacy and immune modulation supports further investigation.

Change in waist circumference from baseline to six-months in patients assigned to POWER-remote and self-directed arms.

Supplementary methods

Supplementary Table and Figure Legends

Gene list and biological pathways of significant differentially expressed genes in hormone-resistant breast cancer volcano plot.

Purpose: The clinical utility of next-generation sequencing (NGS) in breast cancer has not been demonstrated. We hypothesized that we could perform NGS of a new biopsy from patients with metastatic triple-negative breast cancer (TNBC) in a clinically actionable timeframe.Experimental Design: We planned to enroll 40 patients onto a prospective study, Individualized Molecular Analyses Guide Efforts (IMAGE), to evaluate the feasibility of obtaining a new biopsy of a metastatic site, perform NGS (FoundationOne), and convene a molecular tumor board to formulate treatment recommendations within 28 days. We collected blood at baseline and at time of restaging to assess cell-free circulating plasma tumor DNA (ptDNA).Results: We enrolled 26 women with metastatic TNBC who had received ≥1 line of prior chemotherapy, and 20 (77%) underwent NGS of a metastatic site biopsy. Twelve (60%) evaluable patients received treatment recommendations within 28 days of consent. The study closed after 20 patients underwent NGS, based on protocol-specified interim futility analysis. Three patients went on to receive genomically directed therapies. Twenty-four of 26 patients had genetic alterations successfully detected in ptDNA. Among 5 patients, 4 mutations found in tumor tissues were not identified in blood, and 4 mutations found in blood were not found in corresponding tumors. In 9 patients, NGS of follow-up blood samples showed 100% concordance with baseline blood samples.Conclusions: This study demonstrates challenges of performing NGS on prospective tissue biopsies in patients with metastatic TNBC within 28 days, while also highlighting the potential use of blood as a more time-efficient and less invasive method of mutational assessment. Clin Cancer Res; 23(2); 379–86. ©2016 AACR.

Kaplan-Meier curves for survival after disease progression among women with advanced hormone-resistant breast cancer by optional continuation (blue curve) or event monitoring (red curve). The 95% confidence limits are shaded; Tick marks indicate censored data.

Purpose: Although most human cancers display a single histology, there are unusual cases where two or more distinct tissue types present within a primary tumor. One such example is metaplastic breast carcinoma, a rare but aggressive cancer with a heterogeneous histology, including squamous, chondroid, and spindle cells. Metaplastic carcinomas often contain an admixed conventional ductal invasive or in situ mammary carcinoma component, and are typically triple-negative for estrogen receptor, progesterone receptor, and HER-2 amplification/overexpression. An unanswered question is the origin of metaplastic breast cancers. While they may arise independently from their ductal components, their close juxtaposition favors a model that postulates a shared origin, either as two derivatives from the same primary cancer or one histology as an outgrowth of the other. Understanding the mechanism of development of these tumors may inform clinical decisions.Experimental Design: We performed exome sequencing for paired metaplastic and adjacent conventional invasive ductal carcinomas in 8 patients and created a pipeline to identify somatic variants and predict their functional impact, without having normal tissue. We then determined the genetic relationships between the histologically distinct compartments.Results: In each case, the tumor components have nearly identical landscapes of somatic mutation, implying that the differing histologies do not derive from genetic clonal divergence.Conclusions: A shared origin for tumors with differing histologies suggests that epigenetic or noncoding changes may mediate the metaplastic phenotype and that alternative therapeutic approaches, including epigenetic therapies, may be required for metaplastic breast cancers. Clin Cancer Res; 23(16); 4875–84. ©2017 AACR.

Purpose: In breast cancer models, combination epigenetic therapy with a DNA methyltransferase inhibitor and a histone deacetylase inhibitor led to reexpression of genes encoding important therapeutic targets, including the estrogen receptor (ER). We conducted a multicenter phase II study of 5-azacitidine and entinostat in women with advanced hormone-resistant or triple-negative breast cancer (TNBC).Experimental Design: Patients received 5-azacitidine 40 mg/m2 (days 1–5, 8–10) and entinostat 7 mg (days 3, 10) on a 28-day cycle. Continuation of epigenetic therapy was offered with the addition of endocrine therapy at the time of progression [optional continuation (OC) phase]. Primary endpoint was objective response rate (ORR) in each cohort. We hypothesized that ORR would be ≥20% against null of 5% using Simon two-stage design. At least one response was required in 1 of 13 patients per cohort to continue accrual to 27 per cohort (type I error, 4%; power, 90%).Results: There was one partial response among 27 women with hormone-resistant disease (ORR = 4%; 95% CI, 0–19), and none in 13 women with TNBC. One additional partial response was observed in the OC phase in the hormone-resistant cohort (n = 12). Mandatory tumor samples were obtained pre- and posttreatment (58% paired) with either up- or downregulation of ER observed in approximately 50% of posttreatment biopsies in the hormone-resistant, but not TNBC cohort.Conclusions: Combination epigenetic therapy was well tolerated, but our primary endpoint was not met. OC phase results suggest that some women benefit from epigenetic therapy and/or reintroduction of endocrine therapy beyond progression, but further study is needed. Clin Cancer Res; 23(11); 2691–701. ©2016 AACR.

Purpose:We initiated a clinical trial to determine the proportion of breast cancer survivors achieving ≥5% weight loss using a remotely delivered weight loss intervention (POWER-remote) or a self-directed approach, and to determine the effects of the intervention on biomarkers of cancer risk including metabolism, inflammation, and telomere length.Experimental Design:Women with stage 0–III breast cancer, who completed local therapy and chemotherapy, with a body mass index ≥25 kg/m2 were randomized to a 12-month intervention (POWER-remote) versus a self-directed approach. The primary objective was to determine the number of women who achieved at least 5% weight loss at 6 months. We assessed baseline and 6-month change in a panel of adipocytokines (adiponectin, leptin, resistin, HGF, NGF, PAI1, TNFα, MCP1, IL1β, IL6, and IL8), metabolic factors (insulin, glucose, lipids, hs-CRP), and telomere length in peripheral blood mononuclear cells.Results:From 2013 to 2015, 96 women were enrolled, and 87 were evaluable for the primary analysis; 45 to POWER-remote and 42 to self-directed. At 6 months, 51% of women randomized to POWER-remote lost ≥5% of their baseline body weight, compared with 12% in the self-directed arm [OR, 7.9; 95% confidence interval (CI), 2.6–23.9; P = 0.0003]; proportion were similar at 12 months (51% vs 17%, respectively, P = 0.003). Weight loss correlated with significant decreases in leptin, and favorable modulation of inflammatory cytokines and lipid profiles. There was no significant change in telomere length at 6 months.Conclusions:A remotely delivered weight loss intervention resulted in significant weight loss in breast cancer survivors, and favorable effects on several biomarkers.

ER DNA methylation in hormone-resistant tumor biopsies.

Supplemental Table 1

Supplemental Table 1: Clinical and tumor characteristics of long-term responders

Purpose:Metaplastic breast cancer (MpBC) is a rare aggressive subtype that responds poorly to cytotoxics. Median survival is approximately 8 months for metastatic disease. We report results for advanced MpBC treated with ipilimumab + nivolumab, a cohort of S1609 for rare cancers (DART: NCT02834013).Patients and Methods:Prospective, open-label, multicenter phase II (two-stage) trial of ipilimumab (1 mg/kg i.v. every 6 weeks) plus nivolumab (240 mg i.v. every 2 weeks) for advanced MpBC. Primary endpoint was objective response rate (ORR). Secondary endpoints included progression-free survival (PFS), overall survival (OS), and toxicity.Results:Overall, 17 evaluable patients enrolled. Median age was 60 years (26–85); median number of prior therapy lines was 2 (0–5). ORR was 18%; 3 of 17 patients achieved objective responses (1 complete, 2 partial responses; 2 spindle cell, 1 chondromyxoid histology), which are ongoing at 28+, 33+, and 34+ months, respectively. Median PFS and OS were 2 and 12 months, respectively. Altogether, 11 patients (65%) experienced adverse events (AE), including one grade 5 AE. Eight patients (47%) developed an immune-related AE (irAE), with adrenal insufficiency observed in all 3 responders. Responses occurred in tumors with low tumor mutational burden, low PD-L1, and absent tumor-infiltrating lymphocytes.Conclusions:The ipilimumab and nivolumab combination showed no new safety signals and met its primary endpoint with 18% ORR in advanced, chemotherapy-refractory MpBC. All responses are ongoing at >2 to almost 3 years later. The effect of ipilimumab and nivolumab was associated with exceptional responses in a subset of patients versus no activity. This combination warrants further investigation in MpBC, with special attention to understanding mechanism of action, and carefully designed to weigh against the significant risks of irAEs.

Supplemental table S1

Cellular tumor purity for biopsies is greater than 70%. Tumor purity from biopsies was analyzed with the Estimate Package from Bioconductor using R language. The majority (85%) of biopsies have an estimated cellular purity of over 70%, with small differences observed between pre and post-tx biopsies. Patient 17 had both 8-week and 6-months post-tx biopsies. Tx: therapy.

All supplementary figures and tables

Patient characteristics (optional continuation phase)

vcf files for 16 WES samples analyzed in this study

Characterization of pre and post tx biopsies using Genefu and the PAM50 dataset. Paired biopsies (16/19) match with the clinical subtype of the patient's tumor at diagnosis. Treatment did not affect PAM50 subtype. Tx: therapy; HR: hormone-resistant; TNBC: triple-negative breast cancer.

Supplemental Materials and Methods and Supplemental References

Efforts to induce the differentiation of cancer stem cells through treatment with all-trans retinoic acid (ATRA) have yielded limited success, partially due to the epigenetic silencing of the retinoic acid receptor (RAR)-β. The histone deacetylase inhibitor entinostat is emerging as a promising antitumor agent when added to the standard-of-care treatment for breast cancer. However, the combination of epigenetic, cellular differentiation, and chemotherapeutic approaches against triple-negative breast cancer (TNBC) has not been investigated. In this study, we found that combined treatment of TNBC xenografts with entinostat, ATRA, and doxorubicin (EAD) resulted in significant tumor regression and restoration of epigenetically silenced RAR-β expression. Entinostat and doxorubicin treatment inhibited topoisomerase II-β (TopoII-β) and relieved TopoII-β-mediated transcriptional silencing of RAR-β. Notably, EAD was the most effective combination in inducing differentiation of breast tumor–initiating cells in vivo. Furthermore, gene expression analysis revealed that the epithelium-specific ETS transcription factor-1 (ESE-1 or ELF3), known to regulate proliferation and differentiation, enhanced cell differentiation in response to EAD triple therapy. Finally, we demonstrate that patient-derived metastatic cells also responded to treatment with EAD. Collectively, our findings strongly suggest that entinostat potentiates doxorubicin-mediated cytotoxicity and retinoid-driven differentiation to achieve significant tumor regression in TNBC. Cancer Res; 76(7); 2013–24. ©2016 AACR.

Supplemental Figures: Supplementary Figure 1 - Paclitaxel or carboplatin is less effective than doxorubicin in combination with entinostat and ATRA on induction of cell death. Supplementary Figure 2 - Paclitaxel or carboplatin in the combination is less effective than doxorubicin on induction of RAR-β expression; depletion of RAR-β decreases sensitivity to EAD; and transcriptional regulation of RAR-β by TopoII-β Supplementary Figure 3 - EAD decreases the number of CD44+/CD24-/Epcam+ cells and induces expression of differentiation markers Supplementary Figure 4 - EAD potentiates differentiation in vivo. Supplementary Figure 5 - ELF-3 is increased in differentiated stem cell and mediates the entinostat-differentiation effect. Supplementary Figure 6 - EAD targets metastatic samples.

Supplemental Tables: Supplementary Table S1A. Estimated tumor volume of MDA-MB-231 xenografts treated with entinostat, ATRA, and doxorubicin as single and combined therapies. Supplementary Table S1B. Comparison of the estimated tumor volume of MDA-MB-231 xenografts treated with entinostat, ATRA, and doxorubicin as single and combined therapies. Supplementary Table S2A. Estimated tumor volume of SUM-159 xenografts treated with entinostat, ATRA, and doxorubicin as single and combined therapy. Supplementary Table S2B. Comparison of the estimated tumor volume of SUM-159 xenografts treated with entinostat, ATRA, and doxorubicin as single and combined therapy. Supplementary Table S3A. Estimated tumor volume of MDA-MB-231 xenografts treated with entinostat, ATRA, and carboplatin as single and combined therapy. Supplementary Table S3B. Comparison of the estimated tumor volume of MDA-MB-231 xenografts treated with entinostat, ATRA, and carboplatin as single and combined therapies. Supplementary Table S4A. Estimated tumor volume of SUM-159 xenografts treated with entinostat, ATRA, and carboplatin as single and combined therapy. Supplementary Table S4B. Comparison of the estimated tumor volume of SUM-159 xenografts treated with entinostat, ATRA, and carboplatin as single and combined therapy. Supplementary Table S5. Necrosis scores in mouse xenografts. Supplementary Table S6. EAD treatment shows reduced tumor incidence at limiting dilution. Supplementary Table S7. Characteristics of primary patient samples.

Supplemental Figure S1 Legend Supplemental Figure S2 Legend Supplemental Figure S3 Legend Supplemental Figure S4 Legend Supplemental Figure S5 Legend Supplemental Figure S6 Legend

Background: Patients with homologous recombin ation (HR) deficient tumors may benefit from treatment with DNA damaging agents. Markers of genomic instability can be used to identify HR deficiency, including a 3-biomarker Genomic Instability Score (GIS). For patients with ovarian cancer (OC), the FDA-approved GIS threshold for identifying HR deficiency is 42, set as the 5th percentile for BRCA deficient tumors. Recently, a lower 1st percentile cutoff of 33 was explored in OC; this threshold was significantly associated with improved outcome after platinum-based treatment.1,2 Determining an optimal GIS threshold for different types of tumors is crucial, as the GIS distribution may vary between different cancers and even between different cancer subtypes. We propose GIS thresholds for breast cancer separately for triple-negative breast cancer (TNBC) and estrogen receptor-positive (ER+) breast cancer, using the exploratory threshold of 33 for OC as a comparator. Methods: GISs in BRCA deficient tumors were determined for patients newly diagnosed with varying stages of OC, TNBC, or ER+ breast cancer across 5 cohorts (Timms et al,3 TCGA,4 Abkevich et al,5 TBCRC008,6 the OlympiaD trial7). GIS was determined as a combination of loss of heterozygosity, telomeric-allelic imbalance, and large-scale state transitions. BRCA deficiency was defined by loss of function resulting from a pathogenic variant in BRCA1 or BRCA2 or by methylation of the BRCA1 promoter region, with loss of heterozygosity in the affected gene. GIS distributions in different cancer types and subtypes were compared using the Kolmogorov-Smirnov test. A normal distribution was fit to GISs in BRCA deficient ER+ breast tumors. The 1st percentile of the fitted distribution was chosen as the threshold. Results: A total of 561 OC tumors (190 BRCA deficient), 99 TNBC tumors (44 BRCA deficient), and 406 ER+ breast tumors (76 BRCA deficient) were included across the 5 cohorts. When score distributions were evaluated for BRCA deficient tumors, the GIS distribution within ER+ breast cancer was significantly different than for OC (p=9.6x10-5) and TNBC (p=3.2x10-4). This indicates that different GIS thresholds are appropriate for breast cancer subtypes and that the GIS threshold developed for OC is not appropriate for ER+ breast cancer. The 1st percentile of a normal distribution fit in BRCA deficient ER+ breast cancer tumors yields a threshold of 24. Using this threshold, 45.1% (183/406; 75 BRCA deficient, 108 BRCA intact) of ER+ breast tumors were HR deficient. In contrast, the GIS distribution for TNBC was not significantly different than for OC (p=0.77). Using the exploratory threshold of 33, 63.6% (63/99; 44 BRCA deficient, 19 BRCA intact) of TNBC tumors were HR deficient. Conclusions: When compared to OC, the distribution of GIS in BRCA deficient tumors was different for ER+ breast cancer, but not for TNBC. These findings are consistent with the fact that OC and TNBC are known to have similar molecular signatures.8 Exploratory thresholds of 24 for ER+ breast cancer, and 33 for TNBC and OC could be examined to determine if these cutoffs are associated with a benefit from treatment with DNA targeting agents. Clinical validity and utility of these more inclusive 1% thresholds would require demonstration of correlation with clinical outcomes. The threshold difference observed between these cancer subtypes also suggests that cancer or cancer subtype specific thresholds may be needed as evaluations of HR deficiency expands beyond OC to identify candidates for PARP inhibitors. References: 1 Mol Cancer Res. 2018;16(7):1103-11. 2 Cancers. 2021;13(5):946. 3 Br J Cancer. 2012;107(10):1776-82. 4 Nature. 2012;490(7418):61-70. 5 Breast Cancer Res. 2014;16(145):1-9. 6 J Nucl Med. 2015;56(1):31-7. 7 NEJM. 2017;377(17):1700. 8 Int J Mol Sci. 2016;17(5):759. Citation Format: Kirsten M Timms, Lauren Lenz, Chris Neff, Cara Solimeno, Darl Flake, Judy C Boughey, Matthew P Goetz, Andrea Richardson, Anna Maria Storniolo, Alexander Gutin, Roisin M Connolly, Vered Stearns, Jerry S Lanchbury. Identifying homologous recombination deficiency in breast cancer: Genomic instability score thresholds differ in breast cancer subtypes [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 P5-13-09.

Despite advances in breast cancer treatment, residual disease driven by dormant tumor cells continues to be a significant clinical problem. Leukemia inhibitory factor receptor (LIFR) promotes a dormancy phenotype in breast cancer cells and LIFR loss is correlated with poor patient survival. Herein, we demonstrate that histone deacetylase inhibitors (HDACi), which are in phase III clinical trials for breast cancer, epigenetically induced LIFR and activated a pro-dormancy program in breast cancer cells. HDACi slowed breast cancer cell proliferation and reduced primary tumor growth. Primary breast tumors from HDACi-treated patients had increased LIFR levels and reduced proliferation rates compared to pre-treatment levels. Recent Phase II clinical trial data studying entinostat and azacitidine in metastatic breast cancer revealed that induction of several pro-dormancy genes post-treatment was associated with prolonged patient survival. Together, these findings suggest HDACi as a potential therapeutic avenue to promote dormancy, prevent recurrence, and improve patient outcomes in breast cancer.