153P Correlation between disease free survival (DFS) endpoints and overall survival (OS) in elderly patients with human epidermal growth factor receptor 2-negative (HER2–) early breast cancer (eBC)

A previous trial-level meta-analysis validated DFS as a surrogate endpoint for OS in HER2– BC. To shed light on the patient-level associations between DFS endpoints and OS, this study evaluated the correlation between DFS and OS, invasive DFS (IDFS) and OS, and distant DFS (DDFS) and OS in elderly patients with HER2– eBC. Patients aged ≥66 years with stages I–III HER2– BC were identified from SEER-Medicare data (2010–2019). DFS was defined as time from primary surgery to earliest of carcinoma in situ (CIS) of breast, locoregional/distant recurrence, new primary cancer, or all-cause death. IDFS was defined like DFS, excluding CIS. DDFS was defined like DFS, excluding CIS and locoregional recurrence. OS was defined from primary surgery to all-cause death. All endpoints were assessed using Kaplan-Meier analysis. Normal scores rank correlation between each DFS endpoint and OS was estimated separately in hormone receptor-positive (HR+) and triple-negative BC (TNBC) patients. Of 28,655 patients, 90.4% had HR+ BC and 9.6% had TNBC (median follow-up: 4 years). In TNBC, median DFS, IDFS, and DDFS were 3.1, 3.8, and 4.4 years, respectively. In HR+ BC, median DFS, IDFS, and DDFS were 4.5, 5.9, and 6.3 years, respectively. Median OS was not reached (5-year OS, TNBC: 67.7%; HR+ BC: 83.7%). Across cohorts, a significant positive correlation was observed between each DFS endpoint and OS (Table), with the strongest correlation observed between DDFS and OS in TNBC (correlation coefficient: 0.69; 95% confidence interval: 0.65–0.71; p<0.001) and in HR+ BC (0.60; 0.57–0.62; p<0.001).Table: 153PPatient-level correlations between DFS endpoints and OS in patients with HER2– eBC, stratified by breast cancer subtypeDFS endpointsOverall HER2– eBC cohort (N =28,655)Stratification by breast cancer subtypeHR+/HER2– BC (N = 25,899)TNBC (N = 2,756)Normal scores rank correlation [95% CI]P-valueNormal scores rank correlation [95% CI]P-valueNormal scores rank correlation [95% CI]P-valueDFS0.53 [0.50, 0.56]<0.0010.51 [0.48, 0.54]<0.0010.62 [0.58, 0.66]<0.001IDFS0.59 [0.57, 0.61]<0.0010.58 [0.55, 0.60]<0.0010.66 [0.61, 0.70]<0.001DDFS0.61 [0.59, 0.63]<0.0010.60 [0.57, 0.62]<0.0010.69 [0.65, 0.71]<0.001 Open table in a new tab We observed positive, patient-level correlations between intermediate endpoints and OS in HER2– eBC, highlighting the potential utility of these endpoints as surrogates for OS in this population, given validation in trial-level meta-analyses.