Abstract LB408: <i>Bria-</i>ABC vs physician choice in late stage MBC: Early biomarker correlates of the randomized registration trial

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 &amp;lt;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.