Chemotherapy and 21-gene recurrence score testing for older breast cancer patients: A competing-risks analysis

Purpose: To evaluate the effect of the 21-gene recurrence score (RS) assay in breast cancer-specific mortality (BCSM) and decision-making for chemotherapy in older (aged >= 65 years) breast cancer. Methods: We retrospectively included older patients with T1-2N0 and estrogen receptor-positive breast cancer in the Surveillance, Epidemiology, and End Results database. Cox regression model and competing-risks model were used for data analysis. Results: This study included 8524 patients, 1987 (23.3%) had low RS, 5059 (59.4%) had intermediate RS, and 1478 (17.3%) had high RS. Chemotherapy was administrated in 2.0%, 8.6%, and 51.2% for low, intermediate, and high RS cohorts, respectively (P < 0.001). A total of 597 deaths were recorded, including one-quarter of breast cancer-related deaths and three-quarters as competing causes of death. The 5-year BCSM was 5.4%, 4.7%, and 9.1% for low, intermediate, and high RS cohorts, respectively (P < 0.001), using the Cox regression model, and was 0.8%, 0.9%, and 5.2% for low, intermediate, and high RS cohorts using the competing-risks regression, respectively (P < 0.001). RS was independently correlated with BCSM in both prognostic models. The stratified analysis demonstrated that chemotherapy was not correlated with a lower risk of BCSM in intermediate and high RS cohorts in both prognostic models. Sensitivity analyses replicated similar findings after stratification by the year of diagnosis and patients' age. Conclusions: The competing-risks model is useful in dealing with multiple end events for older breast cancer patients. 21-gene RS was independently associated with BCSM. However, chemotherapy did not significantly decrease the risk of BCSM in intermediate and high RS cohorts. (C) 2020 The Author(s). Published by Elsevier Ltd.