Cancer-Specific Survival in Octogenarian Breast Cancer Patients: A Competing Risk Analysis of Prognostic Factors

Background: This study evaluated long-term survival outcomes in breast cancer patients aged ≥80 years, focusing on how prognostic factors change when competing mortality risks are considered. Methods: We retrospectively analyzed 106 octogenarian breast cancer patients treated between 2013 and 2023. Endocrine therapy was evaluated as a treatment-related prognostic factor. Treatment-related prognostic factors were evaluated using multivariable Cox proportional hazards and Fine–Gray competing-risks models. Results: The median age was 82 years, and the median follow-up time was 27.5 months (range, 6–99 months). In the multivariable Cox proportional hazards, biopsy compared with surgery (HR, 0.56; p = 0.037), presence of endocrine therapy (HR, 0.38; p = 0.003), and CCI ≥8 (HR, 9.96; p < 0.001) were independently associated with OS. In the Fine–Gray model, the associations of surgical procedure (p = 0.120) and endocrine therapy (p = 0.081) with breast cancer-specific mortality were no longer statistically significant. CCI ≥8 remained significantly associated with breast cancer-specific mortality (sHR, 3.76; 95% CI, 1.52–9.31; p = 0.004). Conclusions: In octogenarian breast cancer patients, surgery and endocrine therapy were associated with improved OS, but their associations with breast cancer-specific mortality were attenuated after accounting for competing risks. High CCI emerged as the most robust prognostic factor. These findings support incorporating comorbidity burden and competing-risks assessment into individualized treatment decisions in this population.