Post-mastectomy Radiotherapy for pT3N0 Breast Cancers: A Retrospective, Multi-Institution Review.

The role of post-mastectomy radiotherapy for pT3N0 breast cancers remains undefined. The purpose of this study was to report institutional outcomes for women with pT3N0 breast cancers treated with and without post-mastectomy radiotherapy. We collected data from two large tumor registries on pT3N0 breast cancers diagnosed between 1985 and 2014. Kaplan-Meier estimates were used to analyze freedom from local-regional recurrence (FFLR), relapse free survival, and overall survival. This analysis identified 93 women with pT3N0 breast cancers. Of these, 53 received post-mastectomy radiotherapy and 40 did not. Median follow-up was 6.2 years and 5.3 years in the non-post-mastectomy radiotherapy and post-mastectomy radiotherapy cohorts, respectively. Women not undergoing post-mastectomy radiotherapy were more likely to be diagnosed in the 1980s and 1990s and were less likely to receive systemic therapies than women receiving post-mastectomy radiotherapy (p < 0.05). There was a trend toward increased FFLR in the women receiving post-mastectomy radiotherapy (p = 0.15). FFLR in the post-mastectomy radiotherapy cohort was 98% at both 5 and 10 years. For women not receiving post-mastectomy radiotherapy, FFLR was 88% at both 5 and 10 years. Women not receiving post-mastectomy radiotherapy in our study had an isolated local-regional failure rate of 12% at 10 years, despite receiving inferior systemic treatment by current standards. Local-regional control after post-mastectomy radiotherapy for pT3N0 breast cancers was excellent. Further research is needed to define post-mastectomy radiotherapy indications for this patient population when receiving chemotherapy and endocrine therapy in line with current guidelines.