Adoption Patterns and Predictors of De-escalated Adjuvant Therapy for Older Women With Early Stage Hormone Receptor Positive Breast Cancer

Abstract

Breast conserving surgery (BCS) without adjuvant radiation therapy (RT), followed by endocrine therapy (ET) is a proven alternative for older women with stage I hormone receptor-positive (HR+) breast cancer. However, the extent of adoption of the ET-only approach following publication of phase III clinical trial (initially published in 2004 with a median follow-up of 5 years and again in 2013 with a median follow-up of 12.6 years) data in the past decade is unknown. We examined patterns of adjuvant ET and RT treatment among women age 70+ and predictors of radiation use in a large national cohort during the adoption period. We used pooled data from the Surveillance Epidemiology and End Results (SEER)-Medicare with a National Program of Cancer Registries (NPCR)-Medicare linked database to evaluate a cohort of 7,368 women age 70+ with stage I or II, node negative and HR+ breast cancers. Women were diagnosed between 2007 and 2011, received BCS, and no chemotherapy within 12 months of diagnosis. Patients were grouped into those receiving ET only, RT only, or ET+ RT, and the proportion of patients assigned to each treatment was examined by year. Multivariable logistic regression was used to evaluate predictors of treatment assignment. Results: Among stage I patients, 50.6% received RT+ET, while 13.4% received ET only and 20.7% received RT only. 15.3% of stage I patients received no adjuvant therapy after BCS. Among stage II patients, 53.4% received RT+ET, while 15.2% received ET only, 12.9% RT only, and 18.2% received no adjuvant therapy. The proportion of stage I patients receiving RT as part of adjuvant therapy decreased slightly over time but remained high (73.2% in 2007 versus 69.8% on 2011); for stage II patients receipt of adjuvant radiation remained stable over time at approximately 66%. In adjusted analysis of patients who received either ET alone or RT+ET, stage was not an independent predictor of receiving combined therapy. Predictors of receiving ET alone included older age, co-morbid conditions, and grade 1 tumors. Predictors of treatment assignment were generally similar for stage I and II patients, but black women were more likely than non-Hispanic whites to receive ET alone for stage II disease (OR=1.92; 95% CI=1.16,3.16). RT+ET remains the most common adjuvant treatment choice for older women with stage I HR+ breast cancer. Uptake of ET-only adjuvant therapy appears to be low, despite randomized phase III data supporting ET alone as a treatment option. A substantial minority of patients receive neither adjuvant therapy, possibly due to non-initiation of prescribed ET. More work is needed to evaluate the system-level determinants of radiation use in this population, and to understand the reasons for low adoption of radiation-sparing treatment strategies.