Abstract
INTRODUCTION: Radiation therapy (RT) omission is acceptable in older women with early-stage estrogen receptor + breast cancer treated with breast-conserving surgery (BCS) and adjuvant endocrine therapy (AET). However, RT rates in this population remain high, causing concern for overtreatment. Conversely, patients who omit RT and do not complete a course of AET are at risk of undertreatment. In the Pre-Operative Window of Endocrine Therapy to Inform Radiation Therapy Decisions (POWER) trial, participants receive 90 days of preoperative endocrine therapy to assess tolerance before deciding about RT. This study aimed to determine the rates of undertreatment and overtreatment institutionally and among POWER trial participants. METHODS: Data were retrospectively collected from medical records of women aged ≥ 65 years diagnosed with invasive, estrogen receptor +/human epidermal growth factor receptor 2- breast cancer, ≤ 3 cm, who had BCS between 2012 and 2022. Patients were categorized as undertreated (BCS alone), overtreated (BCS + RT + AET), or appropriately treated (BCS + RT or BCS + AET). RESULTS: The cohort included 478 patients, of whom 62 (12.97%) were undertreated, 202 (42.26%) were overtreated, and 214 (44.77%) were appropriately treated. Appropriately treated patients were more likely to be aged 70-79 years (P < 0.0001) and have high health literacy (P = 0.0003). Of the 37 patients (7.71%) in the POWER trial, more were appropriately treated than patients not in the POWER trial (81.1% versus 44.8%) (P < 0.0001). CONCLUSIONS: Despite long-standing guideline changes, RT utilization remains high. This study highlights how a novel patient-centered approach to guide adjuvant therapy decisions may increase the number of appropriately treated patients.