Brufsky, Adam

Importance The NRG Oncology research organization and NSABP B-35 randomized clinical trial prospectively collected margin width data on postmenopausal women with hormone receptor (HR)–positive ductal carcinoma in situ (DCIS) who underwent lumpectomy, whole-breast irradiation (WBI), and randomly assigned adjuvant anastrozole or tamoxifen therapy. This permitted analysis of outcomes per margin width. Objective To analyze the effect of margin width on ipsilateral breast tumor recurrence (IBTR). Design, Setting, and Participants NSABP B-35 was a phase 3, double-blind, randomized clinical trial in which patients were randomized to either 5 years of tamoxifen or anastrozole. Postmenopausal women with HR-positive DCIS and tumor-free margins were eligible. Enrollment was from January 6, 2003, to June 15, 2006, in academic and community hospital members of the NSABP. Study data were analyzed from July 2024 to April 2025. Interventions There were no specific interventions based on lumpectomy margin width. Main Outcomes and Measures Lumpectomy margin width data were prospectively collected within 3 months of randomization. A pathology form classified margins as positive (ink on tumor), close (<1 mm), or negative (≥1 mm). For the negative margin subgroup, closest margin width was stated separately. Thus, an ancillary analysis using 1-mm and 2-mm margin width partitions was performed. Results A total of 3104 postmenopausal women (mean [SD] age, 61 [7.8] years) were enrolled in NSABP B-35. In an ancillary analysis, 2707 patients were included in the 1-mm margin width partition group, and 2546 patients were included in the 2-mm margin width partition group. IBTR was the most common first event, occurring in 90 of 2707 patients (3.3%): 24 of 502 patients (4.8%) with a margin width less than 1 mm and 66 of 2205 patients (3.0%) with a margin width greater than or equal to 1 mm. Ten-year unadjusted cumulative incidence of IBTR events was 5.6% vs 4.0% for margins less than 1 mm vs margins greater than or equal to 1 mm ( P = .04). Using 2 mm as the discriminant threshold for margin width, 39 of 879 patients (4.4%) with margins less than 2 mm and 49 of 1667 patients (2.9%) with margins greater than or equal to 2 mm experienced an IBTR first. Ten-year unadjusted cumulative incidence of IBTR events with margins less than or equal to 2 mm was 5.3% vs 3.8% for those with margins greater than 2 mm ( P = .05). In models adjusting for other patient and tumor factors, margin width was not a significant predictor of IBTR risk (2-mm threshold hazard ratio, 1.33; 95% CI, 0.86-2.06). Conclusions and Relevance Results of this ancillary analysis of the NSABP B-35 trial show that absolute differences in IBTR rates using margin width groupings of less than 1 mm or greater than or equal to 1 mm and margin width groupings of less than 2 mm or greater than or equal to 2 mm in postmenopausal women with HR-positive DCIS receiving lumpectomy, WBI, and adjuvant endocrine therapy were small. Omission of reexcision lumpectomies based on margin widths of less than 1 mm or less than 2 mm can be reconsidered in appropriate patients. Trial Registration ClinicalTrials.gov Identifier: NCT00053898

Abstract Background: We have identified two potentially predictive signatures of palbociclib resistance: the RBsig, composed of E2F1/E2F2 dependent genes, which is associated with genetic loss of RB1, and the ratio between the gene expression levels of CCNE1 to RB1 (CCNE1/RB1). Both signatures have been previously analyzed in vitro and in neoadjuvant and metastatic studies with palbociclib. The present analysis aims to explore the role of RBsig and CCNE1/RB1 in the phase III adjuvant PALLAS trial, which randomized patients to palbociclib plus endocrine therapy, versus endocrine therapy alone. Materials and methods: Gene expression data from PALLAS were generated using the HTG EdgeSeq Oncology BM Panel. Of the 87 genes composing RBsig, 46 were available within the EdgeSeq dataset and were used for the analyses; CCNE1 and RB1 were both available. RBsig was calculated as the mean of the Z-score scaled gene expression (log) of the 46 genes; CCNE1/RB1 was computed as the log ratio between the mRNA expression of CCNE1 and RB1. The prognostic/predictive effect of the continuous signatures in terms of invasive disease-free survival (IDFS), distant recurrence-free survival (DRFS), and overall survival (OS) was evaluated using Cox proportional hazard models. Results: HTG data were available from 2,587 of 5,748 patients from the entire PALLAS intention-to-treat (ITT) cohort. As RBsig and CCNE1/RB1 levels are affected by pre-surgical treatments, we limited the analyses to 1612 pre-treatment samples (530 core biopsies and 1082 surgical specimens) (analysis population). Compared with the entire PALLAS ITT cohort, the analysis population was significantly enriched for patients with low clinical risk (41.3% vs 59.4%) who did not receive prior chemotherapy (17.5% vs 55.9%). In keeping with the PALLAS ITT cohort, no significant benefit from the addition of palbociclib was observed in the analysis population. Higher baseline RBsig or CCNE/RB1 values were significantly and independently associated with worse IDFS (hazard ratio [HR] 1.63, 95% confidence interval [CI] 1.3-2.0; HR 1.22, 95%CI 1.1-1.3, respectively), DRFS (HR 1.94, 95%CI 1.5-2.5; HR 1.26, 95%CI 1.1-1.4, respectively) and OS (HR 1.79, 95% CI 1.3-2.4; HR 1.26, 95%CI 1.1-1.4, respectively) in the analysis population. No predictive effect of palbociclib benefit was observed for either signature in the analysis population, nor according to clinical risk or chemotherapy receipt. Interestingly, higher RBsig was strongly prognostic in patients who did not receive adjuvant chemotherapy (HR 1.83, 95%CI 1.4-2.3) but not in those who received it (HR 1.01, 95%CI 0.6-1.6) (interaction p=0.02) suggesting a potential predictive role of RBsig for chemotherapy benefit. Conclusions: In the PALLAS trial, higher baseline RBsig or CCNE1/RB1 values are associated with worse prognosis, but are not predictive of benefit from palbociclib in the adjuvant setting. RBsig might be associated with differential benefit from chemotherapy. Further study of these biomarkers may strengthen their role in risk stratification.https://acknowledgments.alliancefound.org Citation Format: L. Malorni, D. Hlauschek, E. Mayer, M. Benelli, L. Biganzoli, I. Migliaccio, A. Kermanidis, G. Pfeiler, E. P. Mamounas, A. M. Brufsky, M. Bellet-Ezquerra, K. Clifton, G. Rubovszky, T. Foukakis, M. Goetz, S. Lee, M. Ruiz-Borrego, W. Symmans, K. V. Ballman, F. Liu, J. Machacek-Link, C. Denkert, A. DeMichele, M. Gnant. Prognostic and predictive role of RBsig and CCNE1/RB1 gene-expression signatures for patients with early breast cancer treated with endocrine therapy with or without palbociclib in the PALLAS trial (ABCSG-42, AFT-05, BIG 14-03) [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS2-07-13.

TPS1138 Background: The SV-BR-1-GM breast cancer cell line activates anti-tumor immunity by expressing tumor associated antigens and secreting GM-CSF which enhances dendritic cell activation and promotes adaptive (T-cell mediated) and innate (dendritic and NK cell) immune responses. The cells are also engineered to optimize immune recognition through pt specific HLA antigen matching. SV-BR-1-GM acts through direct antigen presentation and CD4+ T-cell activation and, when combined w/ checkpoint inhibitors (CPIs), has demonstrated clinical benefit in 54 heavily pretreated metastatic breast cancer (MBC) pts. In pts w/ disease progression following CPI therapy, similar or improved progression free survival (PFS) compared to their prior treatment regimen. Disease control following antibody drug conjugates was observed in 40%of pts. Clinical benefit was seen in 5 out of 8 pts w/ untreated intracranial metastases. CD8+ Immuno-PET imaging suggests systemic activation, w/ increased CD8+ tumor infiltrating lymphocytes at both primary and metastatic tumor sites, as well as lymphoid organs. Optimized sequencing of CPI w/ SV-BR-1-GM and its latest phase 3 formulation have shown enhanced clinical outcomes, including improved overall survival (OS) (median 13.4 mos), PFS (3.6 mos), and clinical benefit rate (CBR; 61%).These findings have informed refinements to the ongoing pivotal, registration enabling Phase 3 trial, designed to optimize pt selection and treatment sequencing strategies. Methods: This ongoing multicenter, randomized, open label Phase 3 trial evaluates Bria-IMT + CPI vs. Treatment of Physician’s Choice (TPC) in MBC pts lacking approved curative therapies. Pts are randomized 1:1:1 to Bria-IMT + CPI, TPC, or Bria-IMT monotherapy (discontinued after 150 enrollments to prioritize combination arms). The Bria-IMT regimen consists of: Day -2: Cyclophosphamide 300 mg/m², Day 0: 20M irradiated SV-BR-1-GM cells, Day 2/3: 0.1 mcg pegylated α interferon at each inoculation site. CPI infusion is administered Day -3 to 3. Cycles q3w. TPC regimens follow site specific SOC. Imaging q6w (first 2 cycles), then q8w. Eligibility includes all MBC subtypes, including CNS mets, and permits prior CPI therapy ( >21 days pre-treatment). There will be 100 sites across the U.S., Canada, and ex-North America w/ an enrollment target of 404. The trial is currently active at 59 sites with 217 sub investigators. To date, 67 pts screened: 46 randomized (median age 56 yrs [34–83], median 6 [2–13] prior lines of therapy. The primary endpoint is OS, with an interim analysis at 144 events targeting a hazard ratio of 0.6. Secondary endpoints: PFS, overall response rate, CBR, CNS event free survival, and TWiST. Safety analyses ongoing; pt reported outcomes assess subjective treatment impact. Clinical trial information: NCT03328026 .

TPS1125 Background: Despite the many available treatments for patients (pts) with HR+, HER2– recurrent/metastatic breast cancer (MBC), optimal treatment after progression on CDK4/6 inhibitors (CDK4/6i) is unclear. One possible CDK4/6i resistance mechanism is increased expression of Aurora kinase A (AURKA), a key mitosis regulator associated with poor prognosis. Further implicated in CDK 4/6i resistance, high c-Myc or RB1 loss of function (LOF) are associated with transcriptional co-regulation or synthetic lethality, respectively, with AURKA. Alisertib is a highly selective, reversible, ATP-competitive, orally administered, small-molecule AURKA inhibitor with antiproliferative activity in HR+ BC-derived cell lines and BC xenograft models. Models with elevated AURKA or c-Myc expression, or RB1 LOF show greater alisertib sensitivity. Alisertib had activity in phase 1 and 2 trials, including objective response rates (ORRs) of 19.6–20% and median progression-free survival (PFS) of 5.4–5.6 months alone or with fulvestrant in pts with HR+/HER2–, endocrine-resistant MBC. The most common treatment-related grade ≥3 adverse events (AEs) were neutropenia, anemia, and leukopenia. Methods: ALISCA-Breast1 (NCT06369285) is a randomized phase 2 study. Primary objective: to determine the optimal alisertib dose administered with endocrine therapy (ET) based on AEs and serious AEs per CTCAE v5.0 and efficacy (ORR, duration of response, disease-control rate, PFS, overall survival). Secondary objectives: to identify biomarkers of efficacy and alisertib pharmacokinetics (PK). Key inclusion criteria: ≥18 years; ECOG performance status 0 or 1; confirmed HR+, HER2–, recurrent/metastatic breast adenocarcinoma not amenable to curative therapy; available tumor tissue for biomarker analyses; progression on or after ≥2 prior ET lines in recurrent/metastatic setting; prior CDK4/6i with ET in recurrent/metastatic setting. Key exclusion criteria: prior chemotherapy in recurrent/metastatic setting; prior AURKA-specific or pan-Aurora-targeted agents; unstable brain metastases. Eligible pts will be randomized 1:1:1 to alisertib 30 mg, 40 mg, or 50 mg orally twice daily on days 1−3, 8–10, and 15–17 every 28 days, plus physician’s choice of anastrozole, letrozole, exemestane, fulvestrant, or tamoxifen not previously used in recurrent/metastatic setting or progressed upon in adjuvant setting; ≤50 pts will be enrolled per arm in the USA and Europe. All pts will undergo sparse PK sampling. Tumor tissue will be centrally assessed for biomarkers, including RB1, MYC, TP53, ESR1, PI3K/AKT pathway, HER2 and AURKA genomic alterations/expression levels. The study will determine the optimal alisertib dose to combine with ET and may identify biomarker(s) defining pts with the greatest benefit from alisertib-based therapy. Clinical trial information: NCT06369285 .

Abstract Background: Bria-IMT™ is an allogeneic whole-cell cancer vaccine, designed to stimulate anti-tumor immunity (Chumsri et al 2024 ASCO). Bria-ABC (NCT06072612) is the multicenter, randomized, open-label trial evaluating overall survival (OS) of Bria-IMT™ regimen vs treatment of physician’s choice (PC) in patients with MBC where no meaningful therapy exists. Methods: 3 arm randomized 1:1:1 (Bria-IMT, Bria-IMT+CPI, or PC) in late stage heavily pretreated pts with MBC. Pts can be ECOG <2, Pts w/ CNS mets and/or who have received prior CPI or ADCs are allowed. The Bria-IMT™ regimen includes preconditioning w/ cyclophosphamide (300 mg/m2) on day -2/-3, intradermal SV-BR-1-GM inoculations (x4) on day 0, and interferon at inoculation sites (Days 1-3). CPI (retifanlimab 375 mg) may be given between days -2 to 2. The regimen is administered every 3 weeks (Q3W). Pts randomized to the monotherapy arm (Bria-IMT™ alone) may cross over to the combo arm upon disease progression. Response assessments are planned Q6W for the first cycle, and then Q8W thereafter. Based on prior data, an interim HR of 0.6 at 144 events will constitute early success. Overall study design anticipates 404 total pts. Results: This interim, unaudited data reflects ongoing enrollment and trial feasibility. To date, 61 pts have completed screening, with 40 pts randomized. Screened pts had a median age of 56 (range 35-82). For pts with evaluable data (n=40), median BMI was 25.6 kg/m2 (8.7-45.7) with a median of 6 (2-13) prior lines of therapy. 20 pts (50%) had HR+/HER2- breast cancer, 18 HR-/HER2- (45%), and 2 HER2+ (5%). Baseline ECOG PS were: 0 (55%), 1 (35%), 2 (10%). In biomarker-evaluable pts, circulating tumor cells were present at baseline in 30% (mean: 10.1 cells/mL; range: 0-139), while cancer-associated macrophage-like cells (CAMLs) were present in all pts (mean: 18.3 cells/mL; range: 1-154). In pts with available follow-up data, median change in CAML count from baseline to most recent cycle was -23.5%. In pts with available HLA typing, match distribution was 0 (19%), 1 (35%), 2 (26%), 3 (16%), and 4 (3%), 8 (26%) class 1, 8 (26%) class 2, and 9 (29%) matching both alleles informing potential immune response interactions with Bria-IMT™. Local injection site reaction (DTH), tumor-marker serum level, and circulating cancer cells, will be analyzed across subtypes to further characterize the pt population. The Bria-IMT™ regimen has been generally well tolerated, with no Tx D/C due to adverse events (AEs). The most frequently reported AEs include nausea (30%), constipation (22.5%), injection site rxn (22.5%), and headache (17.5%) w/ no interstitial lung disease reported. Discussion: Bria-ABC enrollment is ongoing. Future analyses will assess OS, PFS, ORR, CBR, QoL, and CNS event-free survival as data becomes available. Expected to close to enrollment by 2025, with final analyses planned for 2026. Citation Format: Saranya Chumsri, Joyce A. OShaughnessy, Azka Ali, Christopher N. Vaughn, Lawrence M. Negret, Adam Brufsky, Regina Stein, Marcela Salgado, Blaise Bayer, Giuseppe Del Priore, Sara A. Hurvitz. Bria-ABC vs physician choice in late stage MBC: Early biomarker correlates of the randomized registration trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr LB408.

TPS1137 Background: BriaCell (BC) human immortalized cell lines have been engineered to trigger robust immune responses and deliver efficacy through diverse mechanisms, including adaptive (involving T-cells) and innate responses (dendritic and NK cells). BC can match patients’ HLA antigens for optimal effectiveness. BC works by several mechanisms, including direct antigen presentation and activation of CD4+ T-cells. When combined with an immune checkpoint inhibitor, the BC regimen has demonstrated clinical benefit in 54 heavily treated MBCs. Most pts whose disease has progressed after checkpoint inhibitor (CPI) therapy showed similar or improved PFS compared to the patient's last treatment regimen. Disease control after prior antibody-drug conjugates (ADCs) has been observed in 40% of patients, and clinical benefit has been seen in 5/7 patients with untreated intracranial metastases. CD8+ Immuno PET shows an increase in CD8+ tumor infiltrating lymphocytes suggesting systemic activation and infiltration into lymphoid organs and metastatic sites. Sequencing of CPI with BC and the latest phase 3 formulation are associated with improved clinical outcomes, including OS (median 13.4 months), PFS, and CBR, which are reflected in the design of this ongoing pivotal registration enabling Phase 3 study [doi:10.1158/1538-7445.sabcs22-p3-07-12]. Methods: Multicenter randomized, open label Bria-IMT regimen (with SV-BR-1-GM cells) plus CPI vs Treatment of Physicians' Choice (TPC) in MBCs with no approved curative therapies available. ECOG <2 allowed with no limit on prior therapies. Eligibility encompasses all MBC subtypes including pts with CNS metastases. Prior immune therapy is allowed if administered more than 21 days before the first cycle of Bria-IMT; treatments within 21 days preclude participation. Initial randomization will be 1:1:1 to the Bria-IMT regimen + CPI (combination), TPC, and the Bria-IMT regimen alone (monotherapy). There will be 100 sites across the US, Canada, and ex-NA for 404 total evaluable pts. The Bria-IMT regimen includes: Day -2 Cyclophosphamide 300mg/m2, Day 0 20 million irradiated SV-BR-1-GM cells intradermally, and 0.1mcg peg α interferon intra-dermally (Day 2 or 3) into each Bria-IMT inoculation site. After the first 150 pts have enrolled, the monotherapy arm will be discontinued. Bria regimen + CPI arms treatment cycles occur q3w. CPI infusion is given every cycle between Day –3 to Day 3 TPC cycle details will be according to the site's SOC. Imaging assessment will be q6w x2 then q8w. The primary endpoint is overall survival with an interim analysis at 144 events targeting a hazard ratio of 0.6. Key secondary endpoints will include PFS, ORR, CBR, CNS event free survival, and TWiST (time without symptoms or toxicities). Safety analysis will be ongoing. Patient-reported outcomes will be incorporated to assess subjective treatment effects. Clinical trial information: NCT06072612 .

Abstract BACKGROUND: Anti-HER2 therapies have transformed the trajectory for patients with HER2-positive (HER2+) MBC. A subset of patients with HER2+ MBC do exceptionally well and remain on maintenance anti-HER2 therapy for many years. However, current therapy is non-curative and patients are treated indefinitely. While these therapies often are well-tolerated, they may cause significant toxicities, are expensive, and typically require frequent infusion and provider visits. Case reports and retrospective series demonstrate that some patients may do well after stopping anti-HER2 treatment. We currently lack prospective data on the likelihood of clinical impact of successful treatment discontinuation, outcomes among patients who progress and restart HER2-directed therapy, and tools to predict who may safely stop therapy. In this study, we will enroll pts with an exceptional response to anti-HER2 therapy. Pts may elect to either continue or stop anti-HER2 therapy and will be followed clinically and radiographically on a protocol-specified schedule. Considering the central role of patients in choosing the study intervention arm, and the unique nature of stopping therapy as a treatment intervention, patient advocates have been deeply involved in the study design to ensure patient concerns are being heard and addressed. We will retrospectively assess minimal residual disease (MRD), measured in plasma, as a biomarker of ongoing response, in a step toward shifting the treatment paradigm for pts with HER2+ MBC. METHODS: STOP-HER2 is a prospective, non-randomized, phase II, multicenter study of either continuation (cohort 1) or cessation (cohort 2) of anti-HER2 therapy in exceptional responders with HER2+ MBC. Eligible patients must have biopsy-proven HER2+ MBC by ASCO/CAP guidelines and must have been receiving first-line anti-HER2 therapy for MBC for at least 3 years without evidence of progressive disease (PD) as determined by the treating investigator. Patients with prior brain-only PD or oligo-PD outside the brain are eligible at least 2 years after local treatment to the central nervous system (CNS) and in absence of subsequent PD. Up to fifty-two participants will be enrolled into cohort 2, and an additional thirty participants enrolled into the cohort 1, at 10 US sites within the Translational Breast Cancer Research Consortium. Co-primary endpoints are the 1-year progression-free survival (PFS) in cohorts 2 and 1, separately. Secondary endpoints include the clinical benefit rate upon re-initiation of anti-HER2 therapy for patients in cohort 2 experiencing PD after treatment discontinuation; and 3-year overall survival in both cohorts. Correlative endpoints include MRD status at baseline and the correlation between MRD dynamics and outcomes. Patient-reported outcomes will be collected and analyzed, including quality of life, illness intrusiveness, financial toxicity, anxiety, and decision regret. The study will use a two-stage design to assess the primary objective of estimating the rate of participants who are free of progression at one year after discontinuing anti-HER2 therapy. If 50% or less are free of progression at one year, stopping HER2 therapy would not be considered a viable treatment plan (null hypothesis). The study is designed to have 80% power to reject the null hypothesis at the 10% type I error rate when 68% of exceptional responders are free of progression at one year after stopping HER2 therapy. STOP-HER2 began enrollment in Q2 2023 (NCT05721248). Citation Format: Heather Parsons, Kathryn Ruddy, Stefania Morganti, Karen Smith, Victoria Attaya, Eliza Kallfelz, Michelle DeMeo, Jamie LaScala, Shirley Mertz, Teri Pollastro, Patricia Spears, Adam Brufsky, Chau Dang, Susan Dent, Ahmed Elkhanany, WIlliam Gwin, Ciara O'Sullivan, Kathy Miller, Sara Nunnery, Elaine Walsh, Anna Maria Storniolo, Sara Tolaney, Nabihah Tayob, Antonio Wolff, Eric Winer, Mothaffar Rimawi, Ian Krop, Nancy Lin. The STOP-HER2 Trial: A Phase 2 Study of Stopping Trastuzumab - Outcomes in Patients with HER2+ Metastatic Breast Cancer (TBCRC 062) [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-20-01.

Abstract Background: Low levels of HER2 expression (HER2-low) have recently emerged as a therapeutic target in patients (pts) with breast cancer (BC). The aim of this study was to evaluate clinical and demographic variables associated with HER2 expression, as well as the value of HER2-low as a prognostic and predictive biomarker for palbociclib benefit in pts enrolled in the PALLAS trial. Methods: The phase III PALLAS trial investigated the addition of palbociclib to adjuvant endocrine therapy (ET) in pts with stage II-III hormone receptor-positive BC. The aims of this analysis are (1) to assess the association between the presence of low levels of HER2 expression with demographic and clinicopathological parameters, (2) to test the prognostic value of HER2-low status on invasive disease-free survival (IDFS), distant relapse-free survival (DRFS), and overall survival (OS) and (3) to assess the value of HER2 expression as a predictive biomarker of response to palbociclib. HER2-low was defined as HER2 immunohistochemistry (IHC) 1+ or IHC 2+ with negative in situ hybridization; all pathologic evaluation was performed locally. Pts with HER2-0 and Her2-low BC were included in this analysis; those with HER2-positive BC or missing HER2 status were excluded. Association of HER2 with other baseline covariates were tested with Chi-squared tests. Prognostic and predictive power of HER2 were assessed with Cox Models. Multivariable models included age, T-stage, N-stage, grade and progesterone receptor (PR) expression. Hazard ratios (HR) and 95% Confidence intervals (CI) are reported. Results: From the original PALLAS intention-to-treat population (N = 5,753), 5304 pts (92.2%) were included in this analysis. Among these, 2,254 pts (42.5%) were classified as HER2 IHC 0 (HER2-0) and 3,050 (57.5%) as HER2-low (1,838 with IHC 1+ and 1,212 with IHC 2+). For this analysis, median follow-up was 59.8 months. Compared to HER2-0, pts with HER2-low tumors had statistically higher estrogen receptor expression levels (mean expression 89.2% vs 88.2%, p = 0.019), lower PR expression levels (65.9% vs 68.2%, p = 0.007). Importantly, HER2-low status varied significantly across 21 participating countries (range 16.7% to 75.6%; p&lt; 0.001) and was more frequent in pts enrolled in North America (63.1%) than in Europe (53.4%) and other regions (53.4%) (p &lt; 0.001). No differences in HER2 expression were observed according to anatomic stage, T-stage, N-stage, histological grade, age, menopausal status, primary surgery type, prior radiation, prior chemotherapy, or baseline performance status. There were no statistically significant differences in IDFS, DRFS or OS according to HER2 status in univariate or multivariable Cox models (prognostic value, HR provided in the Table). There was no significant interaction between the HER2 status and the benefit to palbociclib in IDFS, DRFS or OS (Table). Similar results were obtained when HER2-0 was compared to HER2 1+ and HER2 2+ separately. Conclusions: In this large, prospective and international cohort, no differences were observed in clinical parameters, prognosis, or differential benefit from palbociclib (predictive value) between HER2-0 and HER2-low tumors. Significant geographic variability was observed in the prevalence of HER2-low status, suggesting a high degree of variation in pathologic assessment of HER2 expression without impact on outcomes. Support: AFT, Abbvie Pfizer; Clinicaltrials.gov: NCT02513394 https://acknowledgments.alliancefound.org Citation Format: Guilherme Nader-Marta, Christian F. Singer, Dominik Hlauschek, Angela DeMichele, Paolo Tarantino, Georg Pfeiler, Miguel Martín, Justin Balko, Zbigniew Nowecki, Marija Balic, Adam Brufsky, Arlene Chan, Patrick G. Morris, Tufia Haddad, Sibylle Loibl, Yuan Liu, Lidija Sölkner, Christian Fesl, Erica Mayer, Michael Gnant. Clinical characterization, prognostic and predictive values of HER2-low in early breast cancer in the PALLAS trial [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-01-13.

Abstract Background. The phase 3 PALLAS trial (NCT02513394) compared two years of the CDK4/6 inhibitor palbociclib with endocrine therapy of provider choice, versus endocrine therapy alone, as adjuvant treatment for patients with Stage II-III hormone receptor-positive HER2-negative (HR+/HER2-) breast cancer. Genomic subtype (PAM50 intrinsic subtype) measured from whole-transcriptome RNA sequencing data was defined in the protocol of the PALLAS trial as the primary biomarker for analysis of prediction and prognosis. Clinical data have been previously presented (Gnant et al, JCO 2022), and the trial now has 5-year median follow-up. Methods. As part of trial eligibility, all participants in PALLAS provided a tumor tissue block prior to randomization (surgical if primary resection, core biopsy if neoadjuvant treatment) for translational analyses (TRANS-PALLAS). The biorepository and laboratory were blinded to identity and processed samples in random order, to minimize bias. Nucleic acids were extracted from samples with sufficient tumor tissue and cellularity (&gt;25 mm2 with ≥20% cancer nuclei). The Genome Sequencing Center at Washington University St. Louis performed whole-transcriptome RNA sequencing. Libraries were prepared from 1 µg DNase-1 treated total RNA, if total RNA DV200 &gt;28 (Agilent Bioanalyzer), using an unbiased library protocol of RNA HyperPrep kit with RiboErase (HMR) (Kapa Biosystems, Wilmington, MA). 100 bp paired-end sequencing was performed on NovaSeq 6000 using S4 Reagent Kit (Illumina, San Diego, CA), with 48 libraries pooled per lane. Intrinsic subtype was determined using Bioclassifier package (Research PAM50 script, Parker et al.) only for the analysis population of primary breast cancer samples that had not been exposed to prior neoadjuvant therapy. Invasive disease-free survival (IDFS) will be visualized using Kaplan-Meier plots, with log-rank test between groups. Cox models of proportional hazards will be developed to evaluate prognosis adjusted for known clinical covariates, or for predictive interactions. The pre-defined level of significance is a two-sided 0.05. Results. From the total study population of 5796 enrolled patients, 4655 tissue blocks had sufficient tumor content to process for RNA, with 3931 yielding sufficient RNA for sequencing, and 2669/4655 (57.3%) submitted tissue blocks had DV200 ≥28 and were successfully sequenced. Clinical unblinding revealed 2370 unique patients (1182 in the palbociclib treatment arm and 1188 in the control arm) with intrinsic subtype defined from their untreated primary tumor: 1555 (65.6%) luminal A, 287 (12.1%) luminal B, 167 (7.0%) HER2-enriched, 310 (13.1%) basal-like, 51 (2.2%) normal-like. We will report the results for association of molecular subtype, proliferation score, and Risk of Recurrence (ROR) scores with invasive disease-free survival (IDFS) by treatment arm at the meeting. Conclusions. The TRANS-PALLAS cohort represents one of the largest biorepositories of HR+/HER2- early breast cancer reflecting contemporary systemic management in the framework of a prospectively randomized global trial. Required tumor block submission in this phase 3 trial yielded data from unbiased whole-transcriptome RNA sequencing of the primary tumor prior to treatment from 41% of the PALLAS participants. The proportion of luminal A cancers was unexpectedly high (66%), indicating a lower-risk distribution of cancers in this population. The planned analyses of prediction and prognosis are ongoing and those results will be presented at the time of the meeting. Support: AFT, ABCSG, Pfizer, ECOG-ACRIN, NSABP Foundation, GBG, BIG; Clinicaltrials.gov Identifier: NCT02513394; https://acknowledgments.alliancefound.org Citation Format: Daniel Stover, Dominik Hlauschek, Erica Mayer, W. Fraser Symmans, Mark Watson, Iros Barozzi, Martin Filipits, Karla Ballman, Meritxell Bellet- Ezquerra, Justin Balko, Gabor Rubovszky, Nicholas Zdenkowski, Adam Brufsky, Guenther Steger, Claudine Isaacs, Sibylle Loibl, Fernando Henao, Meredith Regan, Yuan Liu, Christian Fesl, Patrick O'Brien, Angela DeMichele, Michael Gnant, Otto Metzger. Protocol-defined biomarker analysis in the PALLAS (AFT-05) adjuvant trial: Genomic subtype derived from RNA sequencing of HR+/HER2- early breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr GS03-07.

Abstract PURPOSE: Treatment options for patients (pts) with HER2+ BCBM remain limited. We previously reported that neratinib monotherapy is associated with a volumetric central nervous system objective response rate (CNS ORR) of 8%, whereas the combination of neratinib and capecitabine resulted in a volumetric CNS ORR of 49% (in lapatinib-naïve pts). Preclinical data suggest that neratinib may overcome resistance to trastuzumab-emtansine (T-DM1) and that the combination has potential CNS efficacy. Here, we report results of neratinib plus T-DM1 in pts with HER2+ BCBM. PATIENTS AND METHODS: In this prospective, multicenter, phase II study, pts with measurable HER2+ BCBM received neratinib 160 mg orally once daily plus T-DM1 3.6 mg/kg IV every 21 days in three parallel-enrolling cohorts. Cohort 4A enrolled pts with previously untreated brain metastases. Cohort 4B enrolled pts with BCBM progressing after prior local CNS-directed therapy without prior exposure to T-DM1. Cohort 4C enrolled pts with BCBM progressing after prior local CNS-directed therapy who had previous exposure to T-DM1. Diarrhea prophylaxis with colestipol and loperamide was required during cycle 1. Cohorts 4A and 4B were single-stage with a planned enrollment of 20 patients; cohort 4C had a two-stage design, with a requirement for at least 1 of the first 9 pts to achieve a response in order to enroll a total of 24 patients. The primary endpoint was Response Assessment in Neuro-Oncology-Brain Metastases (RANO BM) in each cohort separately. Correlative studies included patient-reported outcomes (PROs) for gastrointestinal toxicity. RESULTS: We enrolled 6, 17, and 21 patients to cohorts 4A, 4B, and 4C, during 11/07/2018 – 11/01/2021. Enrollment was stopped prematurely due to slow accrual. Across Cohorts 4A-4C, the median number of prior lines of chemotherapy prior to enrollment was 2 (range 1-10); 25% received prior lapatinib and no patients received prior tucatinib. In cohorts 4B and 4C (prior CNS-treated cohorts), 33% had prior CNS surgery and &gt;94% had prior CNS radiation. Among evaluable patients, CNS ORR in cohorts 4A (n=6), 4B (n=16), and 4C (n=21) was 50.0% (95% CI 18.8- 81.2%), 25.0% (95% CI 8.3-52.6%), and 38.1% (95% CI 19.0-61.3%), respectively. Median (range) number of cycles completed for 4A, 4B, and 4C was 4.5 (1-15), 4 (range 0-49+), and 6 (0-23); three patients on Cohort 4B remain on protocol therapy (cycles 14, 45, and 49). The overall survival at 12-months for cohorts 4A, 4B, and 4C was 83.3% (95% CI, 58.3-100%), 86.2% (95% CI 70-100%), and 83.3% (95% CI 67.6-100%). Diarrhea was the most common grade 3 toxicity (19.0–33.3% across cohorts); one grade 4 liver function event occurred in cohort 4B. Updated efficacy results will be reported at the meeting; PRO analyses are ongoing. CONCLUSION: Intracranial activity was observed for the combination of neratinib plus T-DM1 across all three enrolled cohorts, including those with prior T-DM1 exposure, suggesting synergistic effects of this treatment combination. Our data provide additional evidence for consideration of neratinib-based combinations in pts with HER2+ BCBM. Citation Format: Rachel Freedman, Siyang Ren, Nabihah Tayob, Rebecca Gelman, Karen L. Smith, Raechel Davis, Alyssa Pereslete, Victoria Attaya, Christine Cotter, Wendy Y. Chen, Cesar Augusto Santa-Maria, Catherine Van Poznak, Beverly Moy, Adam M. Brufsky, Michelle Melisko, Ciara C. O’Sullivan, Nadia Ashai, Yasmeen Rauf, Julie Nangia, Dario Trapani, Jennifer Savoie, Robyn Burns, Antonio C. Wolff, Eric Winer, Mothaffar Rimawi, Ian Krop, Nancy U. Lin. Translational Breast Cancer Research Consortium Trial 022: Neratinib and Trastuzumab-Emtansine for HER2+ Breast Cancer Brain Metastases (BCBM) [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 PD7-03.