Radiation therapy use and outcomes among older women with ER-positive and ER-negative stage I breast cancer.

Objective: We performed a population-based analysis to evaluate changes in patterns of radiation therapy (RT) usage after breast-conserving surgery (BCS) and outcomes among women aged 70 years or older with stage I breast cancer.

Methods: We used the Surveillance, Epidemiology and End Results database to identify 33,350 women aged 70 years or older diagnosed from 1990 to 2008 with stage I invasive ductal breast cancer treated with BCS. Patients were stratified by estrogen receptor (ER) status, and classified by RT modality: external beam RT, brachytherapy (BT), other, or none. Usage frequency for each modality was tabulated from 2000 to 2008 subset. Predictors of omission of RT and use of BT were determined by multiple logistic regression. Cox proportional hazard models were created to evaluate the effect of RT usage on breast cancer-specific mortality.

Results: The use of external beam RT decreased during 2000 to 2008. Omission of RT after BCS increased in patients with ER-positive tumors, whereas use of BT increased for both ER-positive and ER-negative tumors. Predictors for the use of BT were later year of diagnosis, metropolitan residence, and highest income quartile. Omission of use of any RT was associated with increased risk of breast cancer-specific mortality among both ER-positive and ER-negative cancers, with greater effect in ER-negative women.

Conclusions: Among older women with stage I breast cancer treated with BCS, use of any RT has been omitted more frequently and BT utilized more often. Further studies are necessary to evaluate potential under-utilization of RT, particularly among women with ER-negative tumors.