Adjuvant Chemotherapy Outcomes in Older Adults With Nonmetastatic Triple-Negative Breast Cancer

Importance: Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer for which current guidelines recommend adjuvant chemotherapy. Data about the benefit of adjuvant chemotherapy in older women with TNBC are scarce. Objective: To assess the survival benefit of adjuvant chemotherapy in older women with nonmetastatic TNBC. Design, Setting, and Participants: This retrospective population-based cohort study used the Surveillance, Epidemiology, and End Results database from January 1, 2010, to December 31, 2021. Participants included women 70 years or older with nonmetastatic TNBC who underwent surgical removal of breast tumor and were candidates for adjuvant chemotherapy. The median follow-up was 46 (IQR, 21-83) months. Statistical analysis was conducted on August 4, 2025. Exposure: Receipt or nonreceipt of adjuvant chemotherapy. Main Outcomes and Measures: The primary outcome was breast cancer-specific survival between patients who received chemotherapy and those who did not. Logistic regression models assessed variables associated with chemotherapy use. Machine learning with a generalized boosted model was used to estimate propensity scores. Inverse probability of treatment weighting and Cox proportional hazards regression methods were used to compare breast cancer-specific and overall survival. Results: A total of 5730 women (median age, 76 [IQR, 73-81] years) were included in the analysis; 2509 received chemotherapy and 3221 did not. Patients who received chemotherapy were younger (median age, 74 [IQR, 71-77] vs 79 [IQR, 74-84] years) and had more advanced disease (stage II-III, 1388 [54%.5] vs 1664 [51.7%]) than those who did not. Adjuvant chemotherapy was associated with improved breast cancer-specific survival (hazard ratio [HR], 0.69; 95% CI, 0.58-0.82) and overall survival (HR, 0.55; 95% CI, 0.49-0.62). Similar results were observed across subgroups. Increasing age (odds ratio [OR] for 80-89 years, 0.15 [95% CI, 0.13-0.17]; OR for ≥90 years, 0.02 [95% CI, 0.01-0.04]) was associated with lower odds of receiving adjuvant chemotherapy. Conclusions and Relevance: In this cohort study of older women with TNBC, adjuvant chemotherapy was associated with improved survival outcomes. Underutilization of adjuvant chemotherapy in older women may contribute to worse outcomes. Geriatric assessment tools may help guide individualized treatment decisions and promote equitable care.