Priore, Giuseppe Del

e14535 Background: Anti-programmed cell death ligand PD-L1/PD-1 immune checkpoint inhibitors (ICIs) are approved for metastatic breast cancer (mBC) patients (pts) with a tumor combined positive score (CPS) ≥10% in their tissue. However, many pts with < 10% CPS may also respond to ICIs. Recent studies in lung cancer have shown that circulating tumor cells (CTCs) and tumor-macrophage fusion cells (TMFCs) both express, and may upregulate, PD-L1 which is predictive for ICI responses. We initiated a prospective study to monitor PD-L1 in CTCs & TMFCs in mBC pts prior to receiving systemic ICIs to correlate their PD-L1 expression to progression free survival (PFS) and overall survival (OS) at 24 months. Methods: We conducted a multi-institutional prospective pilot study of n = 102 pts with pathologically confirmed mBC, having failed ≥1 prior lines of therapy, prior to receiving ICIs (n = 52 Pembrolizumab, n = 39 Retifanlimab, n = 5 Atezolizumab, and n = 1 Nivolumab). Anonymized blinded peripheral blood samples (7.5ml) were procured prior to ICI induction (T0) and (~40 days after ICI induction (T1). TMFCs & CTCs were isolated using Cellsieve microfilters with average PD-L1 expressions measured then categorized as negative/low or high. Tumor CPS was categorized as negative/low (< 10%) or high (> 10%). We compared TMFC PD-L1 to tissue CPS by linear regression. TMFC/CTC PD-L1 expression and tissue PD-L1 CPS were compared to pts’ PFS and OS by Cox proportional univariate and multivariate analysis over 24 months. Results: Of n = 102 pts, median age = 59 years (range 32-77); 42% (43/102) were ER+, 33% (33/102) were PR+, 5% (5/102) were HER2+, and 56% (57/102) were triple-negative. 32% (32/102) had an ECOG score of 0, 25% (26/102) had ECOG 1, and 43% of scores were unavailable. N = 42 pts had available tumor CPS data, which did not correlate to TMFC/CTC PD-L1 at T0 or T1. Pts with high CPS did not significantly predict for PFS (HR = 0.78; 95% CI, 0.3-1.9; P = 0.7627) nor OS (HR = 0.54; 95% CI, 0.2-1.7; P = 0.4471). Pts with high TMFC/CTC PD-L1 at T0 also did not significantly predict for PFS (HR = 0.74; 95% CI, 0.5-1.2; P = 0.2799) nor OS (HR = 0.84; 95% CI, 0.4-1.6; P = 0.7220). However, of the n = 82 pts who provided T1 samples, high CTC/TMFC PD-L1 at T1 was significant for better PFS (HR = 2.55; 95% CI, 1.6-4.2; P = 0.0004) and better OS (HR = 2.06; 95%CI, 1.1-3.8; P = 0.0309). Conclusions: In this study of mBC pts treated with PD-L1 ICIs, tissue CPS did not correlate with PD-L1 expression in CTCs or TMFCs. Further, neither CPS nor baseline PD-L1 in CTC/TMFCs predicted for clinical outcomes in ICI therapies. However, PD-L1 in CTC/TMFCs ~40 days post-induction of ICI did predict for better response rates. While this study suggests predictive value of monitoring PD-L1 in blood during ICI therapies, further studies are required to refine and validate these findings.

1107 Background: Bria-IMT is an allogeneic whole cell immunotherapy expressing tumor associated antigens and GM-CSF to stimulate adaptive and innate immunity. The phase 3 Bria-ABC trial (NCT06072612) evaluates Bria-IMT + retifanlimab vs physician’s choice in MBC w/ no meaningful therapeutic options. Characterization of on-trial pt experience, including quality of life (QOL) and tolerability, remains clinically relevant yet underreported. We evaluated QoL and toxicity to assess feasibility of home self administration. Methods: EORTC QLQ-C30 at baseline (BL) and subsequent visits. Raw item responses were aggregated into domain scores. Changes quantified as absolute point differences; domain scores defined as medians of constituent items. Lower functional/symptom and higher global scores indicate better outcomes. Wilcoxon matched pairs test assessed change from BL. Missing QoL data handled by observed cases approach. QoL evaluated at BL, V3, V6, and V9. TWiST and TOX summarized descriptively. TOX defined as cumulative time w/ grade ≥3 TEAEs w/o progression; TWiST as time w/o grade ≥3 toxicity or progression. TOX and TWiST constitute component health states for planned QTWiST analysis pending mature OS. Results: At submission, 251 pts screened, 173 randomized, 147 treated. 75% Caucasian, 20% other, 5% not reported; median 6 prior lines (2-15); ECOG 2 -6%; intracranial mets 9%; 42% HR+, 37% TNBC, 12% HER2+. Median 5 QoL assessments/pt completed. 127 pts completed ≥2 assessments. Paired data available at V3 52%, V6 17%, V9 6%. Global health medians BL 5.0, V3 5.0, V6 5.0, V9 4.5. Score maintenance/improvement: @V3 63% (p=0.7), V6 62%, V9 71%. Functional domains: role (BL 1.5, V3 2.0, V6 2.0, V9 2.0; maintenance 62.7% [p=0.02], 52.4%, 71.4%). Physical (BL 1.0, V3 2.0, V6 2.0, V9 2.0; maintenance 68.7% (p=0.002), 47.6% (p=0.03), 71.4%), cognitive (BL 1.5, V3 1.5, V6 1.5, V9 1.5; maintenance 63.6%, 61.9%, 85.7%). Emotional (BL 1.5, V3 1.5, V6 1.5, V9 1.5; maintenance 75.8% (p=0.9), 81.0%, 85.7%). Social (BL 1.5, V3 1.5, V6 2.0, V9 2.5; maintenance 58.5%, 75.0%, 57.1%). Symptoms: nausea/vomiting (1.0 throughout; maintenance V3 73%, V6 86%, V9 86%), fatigue median 2.0 all timepoints; maintenance 61%, 67%, 71%), pain (BL/V3 1.5, V6/V9 2.0; maintenance V3 57% [p=0.03], V6 62% [p=0.9], V9 86%). TWiST and TOX restricted mean 3.12 mo and 0.63 mo, respectively; 83.2% and 16.8% of observed follow-up. Pts w global health maintenance demonstrated longer median TWiST v deterioration (4.3 v 2.7 mo). ECOG stable in 78% (n=99). Conclusions: Heavily pretreated MBC pts in Bria-ABC demonstrated stable global health and key functional domains. Findings support sustained QoL in advanced disease. TWiST demonstrates meaningful benefit w/o significant toxicity. Ongoing follow up will further characterize durability of pt-reported outcomes and clinical correlation. Results support decentralized care and potential home self administration. Clinical trial information: NCT06072612 .

1108 Background: Metastatic breast cancer (MBC) remains limited by resistance and cumulative toxicity in heavily pretreated patients. Bria-IMT combines a whole-cell vaccine (SV-BR-1-GM) with anti-PD-1 (CPI) to enhance tumor antigen presentation and overcome immune exhaustion. SV-BR-1-GM is an irradiated breast cancer cell line engineered to secrete GM-CSF, promoting HLA class I and II antigen presentation and T-cell activation. We identified a subset with durable clinical benefit and biologic correlates. Methods: Phase I/II evaluating the Bria-IMT regimen (SV-BR-1-GM with CPI (pembrolizumab or retifanlimab). In the phase II portion, pts were randomized 1:1 to CPI initiation at cycle 1 (C1) or delayed start at cycle 2 (C2). Two SV-BR-1-GM formulations were administered: IFNγ-stimulated (IFγ) or unstimulated (≠IFγ). Baseline circulating tumor cells (CTCs) and delayed-type hypersensitivity (DTH) responses to SV-BR-1-GM were assessed as biomarkers. Progression free survival (PFS) and overall survival (OS) were analyzed using Kaplan Meier (KM). Subgroup comparisons (CPI sequencing, IP formulation, DTH status, and baseline CTC status) are exploratory. Results: 32 phase 2 pts were randomized: median age 61 (range 41-80); median prior lines 6 (range 2-13); PFS 3.5 mo (95% CI 3.0 - 4.2); OS 9.5 mo (95% CI 7.0 - 17.4). Among CPI C1 vs C2 starts: median OS 13.3 v 7.4mo (HR 0.8; 95% CI 0.4-1.9, p = 0.6); OS KM probability at 12 mo 47% v 58%. Median OS w ≠IFγ v IFNγ IP =16.6 v 9.1 mo (HR 0.58; 95% CI 0.2-1.4, p = 0.23); OS KM at 12 mo 52.4% v 27.3%. DTH+ v DTH- median OS 11.9 v 4.7 mo (HR 0.0009; p = <0.001), OS KM @12 mo 48% v 0%. CTCs <5 v > 5 at baseline had median OS 16.6 v 5.5 mo (HR 0.005; 95% CI 0.0003-0.09, p < 0.001), OS at 12 mo 49% vs 33%. Among long term survivors @12mo, OS probability 44.0% (95% CI 26.2-59.7%) and @24 mo 26% (95% CI 12.1-42.4%). Median follow up 25.8 with PFS 5.4 mo. 5 received ≠IFγ formulation v 1 w IFNγ. All 6 (3 with CPI @C1, 3@C2) experienced delayed type hypersensitivity reaction to inoculation. 67% of long responders matched HLA at >1 allele, 33% no match. Grade ≥3 AEs in 47% of pts, most common injection site rxn, nausea, fatigue; no tx related D/C; no unexpected safety signals. Conclusions: In heavily pretreated MBC, Bria-IMT demonstrated a tolerable safety profile and the emergence of a long-term survivor cohort. Durable survival was observed beyond 12 and 24 months. Differential survival favoring Ph3 formulation, DTH positivity, lower baseline CTC burden, and early CPI sequencing was observed. These findings support prospective validation of DTH and CTC as predictive biomarkers and the continued use of the Ph3 IP formulation in the ongoing phase 3 study Bria-ABC (NCT06072612). Clinical trial information: NCT06072612 .

Abstract Background: Bria-IMT™ is an allogeneic whole cell immunotherapy expressing tumor associated antigens and GM-CSF, designed to stimulate adaptive and innate immune responses. The ongoing multicenter phase 3 Bria-ABC trial (NCT06072612) evaluates Bria-IMT + Retifanlimab vs physician’s choice in pts with metastatic breast cancer who have exhausted standard therapies. Quality of life characterization in this advanced disease setting is clinically relevant yet underreported. Methods: QOL was assessed using the European Organization for Research and Treatment of Cancer QOL Questionnaire Core 30 (EORTC QLQ-C30) at baseline (BL) and treatment visits. Raw item responses (scale: 1 - 4 for functional/symptom items; 1 - 7 for global health ; lower scores = better functional/symptom outcomes; higher scores = better global health) were aggregated into domain scores. Changes from BL were quantified as absolute point differences on response scales and domain level scores are the median of constituent items. Changes from BL assessed using Wilcoxon matched-pairs signed-rank tests. ECOG status assessed at BL and each treatment visit. TEAEs graded per CTCAE. Missing QOL data handled using observed cases approach. We report QoL outcomes at visits (V) BL, 3, 6, and 9 to characterize pt experience during treatment. Results: As of data cut date, 235 pts have been screened, 169 randomized,129 treated. Median age: 60. 74% Caucasian; 18% other; 8% not reported; median 6 prior lines (2-15); ECOG 2: 7%, intracranial mets: 11%. 51% of pts HR+, 37% TNBC, 10% HER2+, 2% not reported. mPFS 2.9 mo (95% CI, 2.3 - 3.7), median of 5 QoL assessments per pt. Of 127 pts who completed ≥2 EORTC QLQ-C30 assessments, 67 (52%), 21 (17%), and 7 (6%) had paired data available at V3, 6, and 9, respectively. Global health status remained stable (median: BL 5.0, V3 5.0, V6 5.0, V9 4.5; 63% of pts reported maintenance or improvement at V3 [p=0.7], V6: 62%, V9: 71%). Functional domains: physical (median: BL 1.0, V3 2.0, V6 2.0, V9 2.0; 68.7% , 47.6% [p=0.03], 71.4% maintenance), role (BL 1.5, V3 2.0, V6 2.0, V9 2.0; 62.7% [p=0.02], 52.4%, 71.4% maintenance), emotional (BL 1.5, V3 1.5, V6 1.5, V9 1.5; 75.8% [p=0.9], 81.0%, 85.7% maintenance), cognitive (BL 1.5, V3 1.5, V6 1.5, V9 1.5; 63.6% [p=0.2], 61.9%, 85.7% maintenance), and social functioning (BL 1.5, V3 1.5, V6 2.0, V9 2.5; 58.5% [p=0.06], 75.0%, 57.1% maintenance). Symptoms: fatigue (median 2.0 at all timepoints; 61%, 67%, 71% maintenance), nausea/vomiting (1.0 throughout; 73% maintenance at V3 [p=0.8], V6 86% , V9 86%), and pain (1.5 at BL and V3, increasing to 2.0 at V6 and V9, w/ 57% maintenance at V3 [p=0.03], V6 62% [p=0.9], and V9 86%. ECOG status remained stable in 78% (n = 99) of pts during treatment. Most common TEAEs were fatigue, nausea, anemia, and constipation; w/ 45% Grade 3 or 4; 84% &lt; grade 3. QoL trends consistent w/ observed ECOG status and AE profiles. Conclusion: Heavily pretreated metastatic breast cancer pts demonstrated stability in overall health status and key functional domains during treatment. These findings are encouraging w/ a meaningful QOL in a population with advanced disease and limited therapeutic options. These observations and AE profile support decentralized clinical trial initiatives including home self-administration. Ongoing follow up will further characterize the durability of pt reported outcomes and their relationship w/ clinical status. Citation Format: Saranya Chumsri, Chaitali Nangia, Adriana Kahn, Lawrence Negret, Carmen Calfa, Blaise Bayer, Giuseppe Del Priore, Tamar Aghajanian, William Williams, Kelly McCann. QOL outcomes in Bria-ABC late stage metastatic phase 3 trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(8_Suppl):Abstract nr CT137.

e13124 Background: Bria-IMT, an allogeneic whole-cell cancer vaccine (SV-BR-1-GM), was administered w/ an anti PD1 checkpoint inhibitor (CPI) to evaluate its safety and efficacy in advanced/metastatic breast cancer (MBC). SV-BR-1-GM breast cancer cells were engineered to directly stimulate anti-tumor immunity through expression of tumor associated antigens and secretion of GM-CSF to enhance endogenous dendritic cell activation. Addition of a CPI potentiates SV-BR-1-GM action by overcoming the immune suppressive tumor microenvironment and may have a differential impact vs monotherapy SV-BR-1-GM. Methods: In this exploratory analysis of the Phase 1 + randomized Phase 2, HLA matching status was assessed to explore potential correlations w/ clinical outcomes. Pts were stratified by overall HLA match by Class I or II (0 vs ≥1 matches), formulation and MBC subtype to assess objective response rate (ORR), clinical benefit rate (CBR), progression free survival (PFS), and overall survival (OS). Partial HLA matching (≥1 Class I and ≥1 Class II allele) was also analyzed. Results: In the total pt population, the ORR was 10%, CBR 56%, PFS 3.2 months and OS 9.9 months. In those pts treated w/ the phase 3 formulation, ORR was 15%, CBR 63%, PFS 3.6 months and OS 13.4 months. Using available HLA data (n = 52), 25% had 0, 34.6% 1, 32.6% 2, and 8% ≥3 matches. While OS and PFS were greater (Undefined vs 8.5 mos ; p = .02) in pts without an HLA match compared w/ those w/ ≥1 match (see Table), ORR and CBR were similar. This was also the case for pts who had 0 HLA Class I matches vs those w/ ≥1 Class I match (15.6 vs 7.2 mos; p = .002). ORR, CBR, PFS and OS were generally similar for pts who had 0 Class II HLA matches vs those w/ ≥1 match. Pts who matched at least at 1 Class I and 1 Class II allele had a higher ORR and CBR than those who matched at a single Class I or a single Class II allele although PFS and OS were similar between the groups. Similar observations were seen for pts treated w/ the phase 3 formulation. Conclusions: Matching at Class I seemed to decrease PFS & OS, but did not have a similar effect on ORR and CBR. Both matched and non matched pts demonstrated favorable OS and response rates. These findings support further investigation into specific mechanisms and the clinical significance of HLA matching in immunotherapy response. A randomized phase 3 trial is ongoing comparing Bria-IMT vs treatment of physician's choice (NCT06072612). Clinical trial information: NCT03328026 . n (Evaluable) % of Cohort Best ORR Best CBR PFS OS Full Cohort 52 (41) 10% 56% 3.2 9.9 No Match (Overall) 13 (10) 25% 20% 60% 4.2 Undefined Any Match (Overall) 39 (31) 75% 6% 55% 3 8.5 MHC Class I No Match / Any Match 27 (20) / 25 (21) 52% / 48% 10% /10% 55% /57% 3.5 / 2.7 15.6 / 7.23 MHC Class II Any Match 27 (19) 52% 11% 63% 3.2 11.4 MHC Class I&II Match 13 (9) 25% 22% 77% 2.8 8.6 Phase 3 Formulation (N=35) 35 (27) 15% 63% 3.57 13.43 No Match (Phase 3 Formulation) 11 (9) 31% 22% 67% 5.6 Undefined MHC Class I&II Match (Phase 3 Formulation) 11 (7) 31% 29% 71% 2.7 7.23

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 .

1096 Background: Bria-IMT is a combination immunotherapy consisting of allogeneic whole cell cancer vaccine (SV-BR-1-GM) administered w/ immune checkpoint inhibitor (CPI). SV-BR-1-GM breast cancer cells are engineered to directly stimulate anti tumor immunity via expression of tumor associated antigens and secretion of GM-CSF to enhance dendritic cell activation. Addition of CPI potentiates SV-BR-1-GM to overcome the immune suppressive tumor microenvironment. Methods: This Ph I/randomized Ph II study evaluated the Bria-IMT regimen in pts w/ metastatic breast cancer; CTX (300 mg/m²) on day -2/-3, SV-BR-1-GM and CPI on Day 0, w/ low dose peg interferon α at inoculation sites on day 2 (±1) . Phase II pts were randomized 1:1 to receive CPI at cycle 1 or cycle 2. Two SV-BR-1-GM formulations (w/ vs w/o IFNγ incubation) were evaluated. Biomarkers included cancer-associated macrophage-like cells, circulating tumor cells, PD-L1 scores, and delayed-type hypersensitivity skin tests. Results: 54 pts (22 Ph I, 32 Ph II) enrolled; 11 received pembrolizumab, 44 retifanlimab (1 crossover). 33 (61%) pts were ER+/PR+/HER2-, 18 (33%) TNBC, 3 (6%) HER2+. Median OS, PFS, ORR, and CBR were evaluated against two pivotal Ph 3 trials, ASCENT 1 (SG in TNBC) and TROPiCS-02 2 (SG in HR+/HER2- MBC) (see Table 1). In randomized pts, C1 vs C2 CPI had PFS (3.7 vs 3.2 mos, P=0.09) and OS (11.4 vs 7.4 mos, P=0.19). Pts receiving Ph 3 formulation (w/o IFNγ; N=37) had greater PFS (3.6 vs 2.6 mos, P=0.01) and OS (13.4 vs 6.9 mos, P=0.01). Bria-IMT was well tolerated w/ no Tx related D/Cs. Conclusions: The Bria-IMT Ph 3 formulation cohort OS was comparable to ASCENT and TROPiCS-02 (13.43 vs 11.8, 14.4 mos), exceeding TPC arms (6.9, 11.2 mos). CBR (61%) compared favorably to ASCENT (40%) and TROPiCS-02 (34%); ORR (14%) matched or exceeded TPC arms (4%, 14%). These outcomes were observed in a more heavily pretreated population, demonstrating Bria-IMT’s clinical activity. Randomized Ph 2 results suggest efficacy and safety in heavily pretreated MBC, w/ no significant OS difference between C1 and C2 CPI initiation and 22% of pts still in active survival follow up. Superior outcomes w/ the Ph 3 formulation support its continued evaluation. A randomized Ph 3 trial is ongoing, comparing Bria-IMT vs treatment of physician’s choice (NCT06072612). Clinical trial information: NCT03328026 . Trial (Cohort) Age (Median, Range) Prior Therapies (Median) OS (Median, mos) PFS (Median, mos) ORR (%) CBR (%) Bria-IMT (Overall Cohort) 61 (38-81) 6 (2-13) 9.9 (1.8-30.3) 3.6 10% 55% Bria-IMT (Ph 3 Formulation) 62 (44-80) 6 (2-13) 13.43 (1.8-30.3) 3.6 (1.8-16.5) 14% 61% ASCENT (SG) 54 (27-82) 4 (2-17) 11.8 4.8 31% 40% ASCENT (TPC) 53 (27-81) 4 (2-14) 6.9 1.7 4% 8% TROPiCS-02 (SG) 57 (49-65) 3 14.4 5.5 21% 34% TROPiCS-02 (TPC) 55 (48-63) 3 11.2 4 14% 22% References: Bardia A et al. J Clin Oncol. 2024 May 20;42(15):1738-1744Rugo, Hope S et al. The Lancet, Volume 402, Issue 10411, 1423 – 1433.

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 &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.

Abstract Background: Bria-IMT™ is a combination immunotherapy consisting of allogeneic whole-cell cancer vaccine (SV-BR-1-GM) administered w/ immune checkpoint inhibitor (CPI). SV-BR-1-GM breast cancer cells have been engineered to directly stimulate anti-tumor immunity through expression of tumor-associated antigens and secretion of GM-CSF to enhance dendritic cell activation. Addition of CPI potentiates SV-BR-1-GM to overcome the immune-suppressive tumor microenvironment. Methods: This Phase I and randomized phase II combination study evaluated the Bria-IMT™ regimen: preconditioning w/ CTX (300 mg/m2) on day -2 or -3, SV-BR-1-GM inoculation and CPI administration on Day 0, and low-dose peg- interferon α at inoculation sites 2 (±1) day post-SV-BR-1-GM. Phase II pts were randomized 1:1 to receive CPI at cycle 1 (immediate) or cycle 2 (delayed). Two SV-BR-1-GM formulations (w/ and w/o IFNγ incubation) were evaluated. Biomarkers included cancer-associated macrophage-like cells (CAMLs), circulating tumor cells (CTCs), PD-L1 scores, and delayed-type hypersensitivity (DTH) skin tests. Results: 54 pts (22 in Phase I, 32 in Phase II) enrolled. 11 pts received pembrolizumab, 44 retifanlimab, w/ 1 pt transitioning from pembrolizumab to retifanlimab. Median age 61(38-81) years; median 6(2-13) prior regimens. 33(61%) pts were ER+/PR+/HER2-, 18(33%) TNBC, and 3(6%) HER2+. Bria-IMT regimen was well tolerated, w/ no attributable Tx D/C. 67% of adverse events grade 1-2; 13% ≥ grade 3 including pulmonary embolism, increased lipase, and dehydration. Median overall survival (OS) was 9.9 (1.8 - 30.3) mos w/ 13% of pts in active survival follow-up. Median progression free survival (PFS) was 3.2 (1.1-16.5) mos w/ 1 pt still in treatment (16.5 mos). Pts treated w/ ph 3 formulation (w/o IFNγ; N = 37) had significantly improved PFS (3.6 vs. 2.6 mos, P=0.01) and OS (13.4 vs. 6.9 mos, P=0.01); in evaluable pts, objective response rate was 14% and clinical benefit rate 61%. Randomized pts receiving ph 3 formulation had not reached median OS. In randomized pts, C1 vs C2 CPI initiation showed greater PFS (3.7 vs. 3.2 mos, P=0.09) and OS (11.4 vs. 7.4 mos, P=0.19). OS in pts w/ no HLA match was undefined vs 8.6 mos in pts w/ any match (P = 0.04). DTH (+) vs (-) correlated w/ greater OS (11.9 vs. 4.7 mos, P= &lt;0.0001) and PFS (3.5 vs. 2.4 mos, P=0.001). Conclusion: Randomized phase 2 Bria-IMT demonstrated efficacy and safety in heavily pretreated MBC. Post-progression survival exceeding median OS in pts still undergoing survival follow-up suggests long-term benefit extending beyond treatment period. C1 vs C2 CPI initiation showed no statistical or clinically significant difference in OS. Superior outcomes w/ phase 3 formulation support its use in future trials. These results confirm earlier reports of the trial and an even greater benefit. A randomized phase 3 trial is ongoing comparing Bria-IMT vs treatment of physician's choice (NCT06072612). Trial Information: NCT03328026 Citation Format: Saranya Chumsri, Chaitali Nangia, Minal Barve, Kendrith Rowland, Ralph Boccia, John Knecht, Blaise Bayer, Marcela Salgado, Tamar Aghajanian, William V. Williams, Charles Wiseman, Giuseppe Del Priore, Carmen Calfa. Survival outcomes in a randomized phase 2 ofBria-IMT: An allogeneic whole cell cancer vaccine [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 CT100.

e13119 Background: Breast cancer metastasis to the central nervous system (CNS) and intracranial area often leads to severe morbidity and mortality. While systemic treatments manage systemic tumors, their impact on CNS/intracranial metastases is limited. Cell based therapies like SV-BR-1-GM may overcome this limitation. SV-BR-1-GM is a GM-CSF secreting, antigen-presenting immortalized breast cancer cell line. We report its efficacy on CNS tumor regression. Methods: Post-hoc analysis of a subset of all advanced MBC patients with CNS/intracranial metastases from previous phase 1, 2, and an ongoing randomized phase 2, trials (n=7 subjects) of SV-BR-1-GM. Bria-IMT monotherapy (intradermal SV-BR-1-GM + cyclophosphamide 300 mg/m2, +interferon-alpha) was administered q3wks to 2 subjects; an immune checkpoint inhibitor (ICI) was administered with each cycle in the combination setting (n=5). Results: There were 7 patients with intracranial metastases at baseline of whom 5 had intracranial tumor responses. Of the 5 responders, median pt age = 66 (range 58-70), median prior lines = 5.5 (3-13), and median time from initial diagnosis = 7.5 years (3-10). 4/5 pts had ≥1 HLA class match with SV-BR-1-GM. 3 were HR + and 1 HER2 +. Pt A002 (ER+/PR+, HER2-) received 6/6 planned cycles, achieving an 83% reduction in breast lesions; after 3 months off therapy, imaging revealed multiple brain metastases and recurrence of right breast lesions. Following 3 additional cycles there was marked regression in both brain and breast lesions. Pt 02-003 (ER-/PR-, HER2 1+ (IHC)) received 5 cycles of SV-BR-1-GM and observed a 60% reduction (5mm -> 2mm) in a left parietal periventricular lesion, and complete resolution (CR) of a left parietal lobe. Pt 06-005 (ER+/PR-, HER2 1+) demonstrated a 56% (9mm -> 4mm) reduction in the thickness of a dural lesion overlying the left anterior temporal lobe after 6 cycles of SV-BR-1-GM + ICI. After 2 additional cycles of SV-BR-1-GM + ICI and 1 cycle of SV-BR-1-GM (ICI skipped on final cycle due to grade 2 AE), patient achieved CR of a left orbital mass observed at baseline (24mm -> 0m). Pt06-007’s (ER-/PR-, HER2 1+) CNS lesions showed a median reduction of 49% compared to baseline after 3 cycles. Pt 11-018 (ER+/PR-, HER2 +) showed standard progression (SD) at initial restaging; 14% increase in sum of diameters of intracranial metastasis. Subsequent imaging, after 3 cycles, showed significant orbital tumor reduction along with reported improvement in eye pain. Conclusions: This post-hoc analysis demonstrated promising efficacy of the Bria-IMT regimen either alone or in combination with ICIs in CNS/intracranial metastasis. The CNS/intracranial regression seen across all breast cancer subtypes among heavily pretreated patients highlights the potential of SV-BR-1-GM in managing CNS metastasis. Ongoing trials will further evaluate the efficacy of the Bria-IMT regimen in patients with CNS/intracranial metastasis. Clinical trial information: NCT03328026 .