ESR1 and neoplasm: All six models in the multivariable analysis, differing in age (continuous; <35 vs. ≥35 years; <45 vs. ≥45 years) and tumor stage (II–III vs. I; III vs. I–II), confirmed tumor stage as the strongest risk factor (Supplementary Table S5) in both groups, while ER-positivity emerged as a statistically significant negative prognostic factor (with an effect comparable with advanced stage) for recurrence in BRCA1/BRCA2 mutation carriers.