Endocrine therapy initiation and overall survival outcomes with omission of radiation therapy in older Medicare patients with early-stage hormone-receptor-positive breast cancer

Background: Guidelines allow for the omission of radiotherapy in older women with early-stage, hormone-receptor-positive breast cancer, given that the patients receive adequate endocrine therapy (ET). However, the initiation of ET and survival outcomes after forgoing radiation therapy among these patients have not been well-studied. Methods: We identified patients aged 70 to 90 years old newly diagnosed in 2010–2015 with early-stage, hormone receptor positive, and human epidermal growth factor receptor 2 (HER2) negative (HR+/Her2−) breast cancer who received lumpectomy and omitted radiation therapy using the SEER-Medicare database. We examined the initiation of ET and the utilization patterns of ET using a multivariable logistic regression. We further examined the overall survival outcomes using Kaplan–Meier estimation and Cox proportional hazard model with inverse probability weighting. Results: Of the 2618 patients, 808 (30.9%) received no ET. The multivariable logistic regression showed that more recent years had better ET initiation (2013–2015 vs. 2010–2012: OR = 1.39, 95% CI:[1.16, 1.66]), while older patients (81–90 vs. 70–80: OR = 0.45, 95% CI:[0.38, 0.54]) were less likely to receive ET. Both the Kaplan–Meier estimation (log-rank p-value<0.0001) and the Cox proportional hazard model with inverse probability weighting (HR = 0.76, 95% CI:[0.58, 0.99]) showed that receiving ET was associated with better overall survival. Conclusion: This population-based study suggests that a sizable proportion of patients who omitted radiation did not receive endocrine therapy and receiving endocrine therapy was beneficial among these patients. Although ET initiation has improved in more recent years, certain patient groups were still especially susceptible to no endocrine therapy.