Radiation therapy utilization and outcomes for older women with breast cancer: Impact of molecular subtype and tumor grade.

Background: Radiation therapy (RT) utilization for elderly women with respect to human epidermal growth factor receptor 2 (HER2) receptor status has not been evaluated. Our purpose was to determine differences in RT utilization and breast cancer specific survival (BCSS) for elderly breast cancer patients with distinct molecular biomarkers.

Methods: The Surveillance, Epidemiology, and End Results database was queried for women ≥70 years of age diagnosed with T1N0M0 breast cancer between 2010 and 2013 receiving breast conservation. Chi-squared analysis was performed to determine the difference in RT utilization between groups. Multivariable logistic regression analysis was performed to determine predictors for RT use. Kaplan-Meier curves were created and the log-rank test done to compare differences in breast cancer specific survival (BCSS) between groups.

Results: A total of 12,312 patients met the inclusion criteria. Receipt of RT for patients with distinct tumor biomarkers was as follows: 55.7% for patients with Estrogen Receptor (ER) +/HER2+; 57.1% for patients with ER+/HER2-; 65.6% for patients with ER-/HER2+; and 69.2% for ER-/HER2- patients (p < 0.001). Factors associated with RT use included ER-/HER2- status, 70-74 years of age, and high grade disease, while adjuvant RT was associated with improve BCSS in ER+/HER2- and ER-/HER2- patients.

Conclusions: Patients 70-74 years old and those with ER-/HER2- are more likely to receive adjuvant RT. Moreover, adjuvant RT is associated with improvements in BCSS in ER+/HER2- and ER-/HER2- patients. Given possible poor compliance with hormonal therapy, the omission of RT in ER + patients, without consideration of HER2 status, should be undertaken with care.