Ernst, Brenda

Abstract Objective The validity of progression-free survival (PFS) as a surrogate for overall survival (OS) in the antibody-drug conjugate (ADCs) era remains uncertain. We evaluated the association between treatment effects on PFS and OS in randomized trials of ADCs for metastatic breast cancer (mBC) and explored the surrogate threshold effect (STE). Methods PubMed, Embase, Cochrane, and ClinicalTrials.gov were searched for published randomized controlled phase II–IV trials evaluating ADCs in mBC and reporting hazard ratios (HRs) for both PFS and OS. A meta-epidemiological approach was used. The primary metric was the ratio of hazard ratios (rHR = HR_PFS/ HR_OS), with rHR < 1 indicating a larger effect on PFS. Trial-level associations were assessed using weighted linear regression (R²) and Spearman’s correlation. Results Twenty-one trials (n = 21; 18 phase III) evaluating nine ADCs were included. The pooled rHR was 0.79 (95% CI, 0.73–0.86), indicating a larger relative effect on PFS than OS. Numerically, the largest discrepancies were observed in triple-negative disease (rHR 0.72) and trials allowing crossover (rHR 0.71). Concordant statistical significance between endpoints occurred in 76% of the trials, whereas 24% showed a significant PFS benefit without OS improvement. The trial-level association between PFS and OS was moderate (R² = 0.62; ρ = 0.67). Conclusion Treatment effects on PFS consistently exceeded those on OS, although effect directions were highly concordant between endpoints. These findings provide an exploratory framework to contextualize the relationship between PFS and OS in ADC trials, requiring further validation in diverse clinical settings.

639 Background: Large cohort studies have shown a survival benefit with the use of GLP1 receptor agonists (GLP1 RA) in cancer patients. The impact of GLP1 RA usage in breast cancer (BC) and the different subtypes is unknown. To investigate the potential influence of GLP1 RA usage on BC survival, a study was conducted on a large institutional database. Methods: A de-identified institutional database identified newly diagnosed Stage I, II, and III BC patients from 2005 to present and use of GLP1 RA. The study compared survival rates for BC patients with and without GLP1 RA and further stratified by BC subtype [ER+HER2-, HER2+, ER-PR-HER2-(triple negative BC (TNBC))], BMI, and age. Kaplan-Meier survival curves were used to estimate overall survival. This study analyzed de-identified data accessed through Mayo Clinic Platform Discover. Per 45 CFR 46.102, this activity did not require IRB review. Data was extracted using an established privacy-preserving protocol and de-identified via expert determination under the HIPAA Privacy Rule. Raw EHR data and other unreported data cannot be shared due to de-identification parameters. Results: 88015 BC patients were identified, of which 3919 (4.5%) received GLP1 RA. The 5-year survival rate was 98.5% with vs 85.5% without GLP1 RA (p-value <0.0001). The survival benefit persisted for different BMI’s and ages: BMI >30 (98.4% vs 85.1%), >25 (98.4% vs 85.4%), and age <50 (99.5% vs 89.3%) and >50 (98.1% vs 84.8%) [all p<0.0001]. 21770 patients with ER+ disease were identified, of which 1412 (6.5%) received GLP1 RA. The 5-year survival rate was 99.0% vs 87.7% (p-value <0.0001). The survival benefit persisted by BMI and age: BMI >30 (99.0% vs 86.2%), >25 (98.9% vs 87.1%) and age <50 (99.6% vs 90.5%) and >50 (98.7% vs 87.2%) [all p<0.0001]. 3599 patients with HER2+ disease were identified, of which 202 (5.6%) received GLP1 RA. The 5-year survival rate was 99.3% vs 80.1% (p-value <0.0001). The survival benefit persisted by stratification: BMI >30 (100.0% vs 80.0%, p-value <0.0004), and <25 (97.7% vs 76.2%, p-value <0.019), and age <50 (100% vs 87.0%, p-value <0.043) and > 50 (99.0% vs 77.2%, p-value <0.0002). 8389 patients with TNBC disease were identified, of which 360 (4.3%) received GLP1 RA. The 5-year survival rate was 91.0% vs 71.9% (p-value <0.0001). The survival benefit persisted by stratification: BMI >30 (96.4% vs 72.9%, p-value <0.0001), >25 (93.2% vs 71.8%, p-value <0.0001), and age <50 (96.0% vs 73.0%, p-value <0.0028) and >50 (88.9% vs 71.8%, p-value <0.0001). For those TNBC patients who received GLP1 RA, having a BMI >30 conferred a protective effect with a 5-year survival rate was 97.9 vs 89.8% (p-value <0.0014). Conclusions: The study suggests that GLP1-RA improves 5-year survival rates of patients with BC and this applies to all subtypes of BC. These results suggest that further study of the impact of GLP1-RA on BC patients is warranted.

536 Background: Folate receptor alpha (FRα) is overexpressed in ~80% of triple-negative breast cancers (TNBC). We previously demonstrated that patients (pts) with breast cancer naturally mount immune responses to FRα. In prior Phase I and II studies, a GM-CSF-adjuvanted FRα peptide vaccine (FRPV) was safe and induced durable FRα-specific T-cell immunity in 83–90% of pts with breast and ovarian cancer. Methods: Eligible pts were women ≥18 years with TNBC (ER/PR ≤10%) with 1+ of the following: stage ≥T1c disease, node-positivity, or residual disease after neoadjuvant chemotherapy. Pts were randomized 2:1 to receive FRPV or placebo (GM-CSF alone) every 28 days for cycles 2-7 and then every six months for 7 booster doses, with cycle 1 consisting of cyclophosphamide 50mg orally twice daily for days 1-7 and 15-21 (in both arms). Randomization was stratified by chemotherapy setting (adjuvant only vs neoadjuvant) and stage (I/II vs III). FRα expression was evaluated by immunohistochemistry. The study was designed to detect (at 30 months after the last pt enrolled) a disease-free survival (DFS) difference of 14% assuming a 3.5-year DFS rate of 70% in the control group and with 78% power. Results: 280 pts were enrolled (median age 52). The majority had stage I or II tumors (n = 219, 78%). There were numerically more node-positive tumors in the vaccine arm, 78 (41%) vs 27 (32%), p = 0.15. Median follow-up was 3.5 years, and 33 (FRPV: 25, placebo: 8) DFS events were observed; 3.5-year DFS rate was 88% with FRPV and 90% with placebo (HR 1.42, 95% CI 0.64–3.15; p = 0.39). Overall survival (OS) also did not differ by arm (HR 2.48, 95% CI 0.55–11.20; p = 0.22). Among node-positive pts (n = 105), DFS did not differ between arms (HR 0.95, 95% CI 0.34–2.66; p = 0.92). However, a numerical DFS event rate improvement (14% for vaccine vs. 26% for placebo) was observed in 61 patients with stage III disease (HR 0.51, 95% CI 0.16–1.68; p = 0.26). DFS did not differ by chemotherapy setting or by receipt of anthracycline, capecitabine, and/or an immune checkpoint inhibitor. FRPV was well tolerated, with predominantly grade 1–2 adverse events (AEs) and no vaccine-related grade ≥4 AEs. FRα expression was available from tumor in 230 pts, with 72% expressing > 0. Overall, DFS was not significantly associated with FRα expression (0 vs > 0; HR 0.55, 95% CI 0.21–1.44; p = 0.21), and no significant differences in DFS by FRα expression were observed between treatment arms. Conclusions: FRPV following oral cyclophosphamide was safe, with no vaccine-related high-grade AEs. While no significant improvement in DFS or OS was observed overall, a numeric trend toward improved DFS was observed in pts with stage III TNBC. This finding is hypothesis-generating and supports further evaluation of FRα-targeted vaccination in higher-risk TNBC. Immune correlative analyses are ongoing to better define vaccine immunogenicity and its relationship to clinical outcomes. Clinical trial information: W81XWH-15-1-0293.