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PURPOSE Combining standard of care (pertuzumab-trastuzumab [PH], chemotherapy) with cancer immunotherapy may potentiate antitumor immunity, cytotoxic activity, and patient outcomes in high-risk, human epidermal growth factor receptor 2 (HER2)–positive early breast cancer. We report the phase III IMpassion050 primary analysis of neoadjuvant atezolizumab, PH, and chemotherapy in these patients. METHODS Patients with a primary tumor of > 2 cm and histologically confirmed, positive lymph node status (T2-4, N1-3, M0) were randomly assigned 1:1 to atezolizumab/placebo with dose-dense doxorubicin/cyclophosphamide, followed by paclitaxel, and PH. After surgery, patients were to continue atezolizumab/placebo and PH (total: 1 year of HER2-targeted therapy); those with residual disease could switch to ado-trastuzumab emtansine with atezolizumab/placebo. Coprimary efficacy end points were pathologic complete response (pCR; ypT0/is ypN0) rates in intention-to-treat (ITT) and programmed cell death-ligand 1 (PD-L1)–positive populations. RESULTS At clinical cutoff (February 5, 2021), pCR rates in the placebo and atezolizumab groups in the ITT populations were 62.7% (n = 143/228) and 62.4% (n = 141/226), respectively (difference –0.33%; 95% CI, –9.2 to 8.6; P = .9551). The pCR rates in the placebo and atezolizumab groups in patients with PD-L1–positive tumors were 72.5% (n = 79/109) and 64.2% (n = 70/109), respectively (difference –8.26%; 95% CI, –20.6 to 4.0; P = .1846). Grade 3-4 and serious adverse events were more frequent in the atezolizumab versus placebo group. Five grade 5 adverse events occurred (four neoadjuvant, one adjuvant; two assigned to study treatment), all with atezolizumab. Overall, the safety profile was consistent with that of atezolizumab in other combination studies. CONCLUSION Atezolizumab with neoadjuvant dose-dense doxorubicin/cyclophosphamide–paclitaxel and PH for high-risk, HER2-positive early breast cancer did not increase pCR rates versus placebo in the ITT or PD-L1–positive populations. PH and chemotherapy remains standard of care; longer follow-up may help to inform the long-term impact of atezolizumab.

LBA3 Background: About 55% of mBC typically categorized as HER2 negative, express low levels of HER2 (IHC 1+ or IHC 2+/ISH− by ASCO/CAP 2018 guidelines) with poor outcomes in later lines (Tarantino 2020). T-DXd has shown promising efficacy in HER2-low mBC in a phase 1 study (NCT02564900; Modi 2020). This is the primary report from DESTINY-Breast04 (NCT03734029), the first randomized, multicenter, open-label, phase 3 study comparing efficacy and safety of T-DXd vs TPC in pts with HER2-low mBC treated with 1-2 prior lines of chemotherapy in the metastatic setting. Methods: 557 pts with centrally confirmed HER2-low mBC were randomly assigned 2:1 to T-DXd 5.4 mg/kg or TPC (capecitabine, eribulin, gemcitabine, paclitaxel, or nab-paclitaxel). The primary endpoint was progression-free survival (PFS) determined by blinded independent central review (BICR) in pts with hormone receptor–positive (HR+) mBC. Key secondary endpoints (hierarchically tested after the primary endpoint) include PFS by BICR in the full analysis set (FAS; HR+/−) and overall survival (OS) in pts with HR+ mBC and in FAS. Other endpoints were objective response rate, duration of response, safety, and an exploratory analysis of pts with HR− mBC. Results: As of Jan 11, 2022, 373 and 184 pts (88.7% and 88.6% HR+ mBC) were assigned to T-DXd and TPC, respectively. Median follow-up was 18.4 months (mo; 95% CI, 17.9-19.1). Median treatment duration was 8.2 mo (range, 0.2-33.3) with T-DXd and 3.5 mo (range, 0.3-17.6) with TPC. Efficacy results are in the Table. 52.6% of pts with T-DXd vs. 67.4% of pts with TPC had grade (G) ≥ 3 treatment-emergent adverse events (TEAEs). With T-DXd, 45 pts (12.1%; 10.0% G1/2, 1.3% G3/4, 0.8% G5) had independently adjudicated drug-related interstitial lung disease [ILD]/pneumonitis vs. 1 pt (0.6% G1) with TPC. Conclusions: DESTINY-Breast04 is the first phase 3 trial of a HER2-directed therapy in pts with HER2-low mBC to show a statistically significant and clinically meaningful benefit in PFS and OS compared to standard-of-care treatment, regardless of HR status, with a generally manageable safety profile. Funding: Daiichi Sankyo, Inc., and AstraZeneca. Clinical trial information: NCT03734029. [Table: see text]

1087 Background: Approximately 50% of BCs traditionally categorized as HER2 negative (HER2-neg) express low levels of HER2 (IHC 1+ or IHC 2+/ISH-; Miglietta, NPJ Breast Cancer 2021). HER2-targeted therapies for HER2-low metastatic BC (mBC) are under investigation (eg, T-DXd in the phase 3 DESTINY-Breast04 study; NCT03734029), but HER2 assays currently used to select patients (pts) for approved anti-HER2 therapies are optimized for high HER2 expression and are not validated for HER2-low detection. A recent study found relatively poor agreement (

TPS1103 Background: Modulating estrogen synthesis and/or ER activity is the mainstay of treatment for pts with ER+ BC. Despite substantial progress, many pts experience relapse during/after adjuvant endocrine therapy. However, even though resistant to aromatase inhibitors (AIs) or tamoxifen, growth and survival of the majority of tumors are thought to remain dependent on ER signaling. Therefore, pts with ER+ BC can still respond to second- or third-line endocrine treatment after progression on prior therapy (Di Leo 2010; Baselga 2012). Therapeutic resistance can arise from mutations in ESR1, which can drive estrogen-independent transcription and proliferation. The highly potent, non-steroidal oral selective ER degrader giredestrant achieves robust ER occupancy and is active regardless of ESR1 mutation status. Phase I data indicate that giredestrant is well tolerated, with encouraging activity as a single agent and in combination with the CDK4/6 inhibitor palbociclib (Lim 2020). Single-agent activity was observed after prior treatment with fulvestrant and/or a CDK4/6 inhibitor (Jhaveri 2019). Methods: persevERA BC (NCT04546009) is a double-blind, placebo-controlled, randomized, multicenter phase III study designed to evaluate the efficacy and safety of first-line giredestrant + palbociclib in pts with ER+/HER2– LA/mBC. Randomization: 1:1 to either giredestrant (30 mg PO) plus letrozole placebo QD or letrozole (2.5 mg PO) plus giredestrant placebo QD on Days 1–28 of each 28-day cycle, with palbociclib (125 mg PO QD) on Days 1–21 of each 28-day cycle. Men and premenopausal women will receive an LHRH agonist. Eligibility: females or males ≥18 years old with measurable disease or evaluable bone disease and no prior treatment for advanced disease. Pts who received prior fulvestrant or who have relapsed within 12 months of completion of (neo)adjuvant therapy with an AI and/or prior therapy with CDK4/6 inhibitor are not eligible; relapse during tamoxifen therapy but > 24 months after the start of tamoxifen therapy is allowed. Stratification: site of disease, disease-free interval since the end of (neo)adjuvant therapy, menopausal status, and geographic region. Primary efficacy endpoint: progression-free survival (determined locally by the investigator per RECIST v1.1). Secondary endpoints include overall survival, objective response rate, duration of response, clinical benefit rate, QoL, and safety. Enrollment is open (first patient in: Oct 9, 2020); target recruitment is 978 pts across all sites in a global enrollment phase. After completion of the global enrollment, additional pts may be enrolled in China. Clinical trial information: NCT04546009 .

TPS1100 Background: Systemic chemotherapy with anti-HER2 therapy is the standard of care for HER2-positive advanced breast cancer. Patient outcomes have improved remarkably with the use of novel anti-HER2 drugs, including trastuzumab (H), pertuzumab (P), and trastuzumab emtansine (T-DM1). The combination treatment comprising H, P, and docetaxel (D) (HPD) is highly recommended as the 1st-line treatment for patients with HER2-positive advanced breast cancer. In contrast, for elderly patients over 65 years of age, this regimen seems to be intolerable mentally and physically, and impairs their quality of life. A new standard treatment with less toxicity and non-inferior efficacy for elderly patients is needed. Methods: We have planned a randomized, multicenter, open-label, phase III trial to confirm the non-inferiority of T-DM1 compared to HPD in terms of overall survival (OS) in elderly patients with HER2-positive advanced breast cancer. The eligibility criteria are as follows: 1) histologically proven metastatic breast cancer, 2) age 65-74 years with a performance status (PS) score 0-2, or 75-79 years with a PS score 0-1, 3) HER2 overexpression or amplification confirmed in primary or metastatic tissues, and 4) no anti-HER2 therapy with chemotherapy for breast cancer, excluding (neo) adjuvant therapy. Patients are randomized to receive either HPD (H 6 mg/kg, P 420 mg/body, and D 60 mg/m2) or T-DM1 3.6 mg/kg every 3 weeks. The dose up of D (75 mg/m2) after the second cycle is defined based on the data regarding safety during the first cycle. The primary endpoint is OS. The secondary endpoints are progression-free survival, response rate, adverse events, breast cancer-related death, and deterioration of activities of daily living. The trial is designed to achieve 70% power to confirm non-inferiority of T-DM1 to HPD at a one-sided alpha of 5% with a non-inferiority margin of 1.3 in terms of hazard ratio. With a median OS of 30 months in both arms, 6 years of accrual, and 5 years of follow up, the planned sample size is 330. The trial began in January 2018 and nineteen patients have been enrolled as of January 2019. Clinical trial information: UMIN000030783.

Purpose We evaluated whether patients with human epidermal growth factor receptor 2 (HER2) –positive primary breast tumors had metastatic tumors that were HER2 positive (concordant) or HER2 negative (discordant). We then evaluated whether treatment with trastuzumab or chemotherapy before biopsy of the metastasis had any effect on the rate of HER2 discordance. We also compared the overall survival durations of patients with HER2-concordant and -discordant tumors. Patients and Methods We retrospectively identified all patients who initially had been diagnosed with HER2-positive (immunohistochemistry 3+ and/or fluorescent in situ hybridization positive) primary breast cancer between 1997 and 2008 at MD Anderson Cancer Center who also had metastatic tumor biopsy results available for review. Results We included 182 patients who met our criteria. Forty-three (24%) of the 182 patients with HER2-positive primary tumors had HER2-negative metastatic tumors. The HER2 discordance rates differed significantly on the basis of whether patients received chemotherapy (P = .022) but not on the basis of whether patients received trastuzumab (P = .296). Patients with discordant HER2 status had shorter overall survival than did patients with concordant HER2 status (hazard ratio [HR], 0.43; P = .003). A survival difference remained among the 67 patients who received trastuzumab (HR, 0.56; P = .083) and 101 patients who did not (HR, 0.53; P = .033) before their metastasis biopsies. Conclusion We confirmed that loss of HER2-positive status in metastatic tumors can occur in patients with primary HER2-positive breast cancer. Our data strongly support the need for biopsies of metastatic lesions to accurately determine patient prognosis and appropriate use of targeted therapy.

e13090Background: Younger patients with early stage breast cancer have been reported to have worse prognosis compared to older patients while reverse relationship has been demonstrated in stage IV ...

1081 Background: In patients with brain metastasis (BM) of melanoma or lung cancer, significant activity of immune checkpoint inhibitors has been reported. However, details of the immune microenvironment in BM has not been unveiled. In this study, we used immunohistochemistry (IHC) to compare primary breast tumors and BM tumor samples with respect to tumor infiltrating lymphocytes (TILs) and tumor characteristics related to the immune system. Methods: We retrospectively identified 107 patients with breast cancer, diagnosed with BM, who had undergone surgery between 2001 and 2012 at 8 institutions. We collected 191 samples which included both BM samples alone and pair-matched samples (primary and BM). Hematoxylin and eosin (H&E) stained slides were evaluated for stromal TILs in 10% increments (0–1%, > 1– < 10%, 10%–100%). IHC was performed using the following primary antibodies: CD4, CD8, Foxp3, PD-L1, PD-L2 and HLA class I. The cells positive for each antibody signal were counted automatically using ImageJ (NIH). The expression of PD-L1, PD-L2, and HLA on the tumor cells was scored as 0 (negative), 1 (weak or focal), or 2 (strong). Results: The median category of TILs of BM tumors was > 1– < 10% (range: 1–30%). Forty-six pair-matched samples were analyzed and the percentage of TILs in the primary breast tumor was significantly higher than that in BM samples (paired t-test, P < 0.01). The number of CD4/CD8/Foxp3 positive cells in primary breast tumor was also significantly higher than in BM samples (paired t-test, P < 0.05 for all categories). The negative/positive conversion occurred with the expression of HLA/PD-L2 on tumor cells (paired t-test, P = 0.03/0.06, respectively). No significant difference was observed in the overall survival (OS) of patients, from initial BM, based on high or low TILs (log-rank test, P = 0.131). However, triple negative breast cancer patients with low TILs had significantly shorter OS compared with patients with high TILs (log-rank test, P = 0.04). Conclusions: We demonstrated that TILs in BM tumors was significantly lower as compared to primary breast tumors. The expression of immune related molecules on tumor cells was converted in BM tumors.

TPS636Background: Combination of pertuzumab (Pmab) with trastuzumab (Tmab) has dramatically improved patients’ outcomes compared to Tmab as 1st line therapy in HER2-positive (+ve) locally advanced ...

e11612 Background: Higher tumor-infiltrating lymphocytes (TILs) in HER2+ early breast cancers have been associated with higher pCR rate and better outcome, with the major attention at the group wit...

588 Background: Recently, neoadjuvant chemotherapy has become a treatment of choice in clinics. Estrogen receptor (ER), progesterone receptor (PgR), and human epidermal growth factor receptor 2 (HE...

11021 Background: The assessment of tumor-infiltrating lymphocytes (TILs) in primary breast cancer allow to predict prognosis and chemotherapy benefit, particularly in triple-negative (TN) and HER2-positive breast cancer. In the latter, it predicts also benefit from HER2-targeted agents. A little is known about the change of TILs during the metastatic progression. We compared TILs in paired samples from primary and metastatic TN and HER2-positive tumors. Methods: We retrospectively identified 25 patients with triple-negative or HER2-positive early breast cancer diagnosed between 1990 and 2010 at a single institution and subsequently experienced a distant recurrence confirmed by tumor biopsy/resection. Hematoxylin- and eosin-stained slides for these paired match cases were evaluated for stromal-TILs as recently recommended (Salgado R Ann Oncol 2014). We defined three groups according to : low-TILs ( ≤ 5), intermediate-TIL (10-50), Lymphocyte Predominant Breast Cancer (LPBC) ( ≥ 60%). Results: We evaluated ...

545 Background: Studies have suggested that trastuzumab may convert HER2-positive (HER+) primary breast tumors to HER2-negative (HER2–). Whether this conversion happens between primary and metastat...

616 Background: Tyrosine 1248 is one of the autophosphorylation sites of HER2. Our goal was to determine the prognostic value of expression level of tyrosine 1248-phosphorylated HER2 (pHER2) in pat...