Adjuvant Chemotherapy and Survival in Older Women With Hormone Receptor–Negative Breast Cancer: Assessing Outcome in a Population-Based, Observational Cohort

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Abstract
Purpose: For older breast cancer patients, there is limited evidence of the efficacy of adjuvant chemotherapy from randomized clinical trials. Our goal wastoassess the relationship between adjuvant chemotherapy use and survival in a large, population-based cohort of older women with hormone receptor (HR) –negative breast cancer. Methods: We identified women age 66 and older diagnosed with HR-negative, nonmetastatic breast cancer from 1992 to 1999 in the Surveillance, Epidemiology and End Results (SEER) cancer registries. Chemotherapy use was identified in Medicare claims linked to SEER records. Clinical and sociodemographic predictors of chemotherapy use were identified using logistic regression. The effect of chemotherapy on survival was evaluated using propensity score methods and multivariable proportional hazards regression. Results: A total of 1,711 (34%) of 5,081 women with HR-negative breast cancer received chemotherapy within 6 months of cancer diagnosis. Chemotherapy use decreased with increasing age and comorbidity, and increased with year of diagnosis, tumor size, number of positive lymph nodes, and higher tumor grade. Adjuvant chemotherapy was associated with a mortality reduction of approximately 15% whether analyzed using propensity scores or standard multivariable methods. The greatest overall survival benefit was observed in patients with node-positive disease and in the node-negative patients most likely to receive chemotherapy. Conclusion: This analysis suggests a survival benefit from adjuvant chemotherapy in older women with HR-negative breast cancer. The benefit of chemotherapy is most pronounced in the patients most likely to be selected for treatment, including those with involved lymph nodes or other high-risk disease characteristics.