Revisiting the impact of age and molecular subtype on overall survival after radiotherapy in breast cancer patients.

Adjuvant radiotherapy (RT) in breast cancer (BC) is often used to eradicate remaining tumor cells following surgery with the goal of maximizing local control and increasing overall survival. The current study investigated the impact of age and BC molecular subtype on overall survival after RT using a meta-analysis of the METABRIC and TCGA BC patient cohorts. We found that RT significantly prolonged survival across the whole BC patient population. The survival benefit of RT was predominantly observed in stage II BC patients treated with breast conserving surgery. Patients were then stratified by age and molecular subtype to investigate survival rate associated with RT. An increase in survival for the luminal-A and basal BC molecular subtypes was observed after RT. Stratifying patients based on age revealed that increased survival was restricted to younger patients (≤60 years of age at diagnosis). There was a significant survival benefit of radiotherapy for younger patients with tumors of the luminal A and basal molecular subtypes. Patients with other breast tumor subtypes or older breast cancer patients did not seem to benefit effects of RT. Therefore, alternate local treatment strategies should be considered for older, luminal B, and HER2 driven BC patients.