Postmastectomy Radiotherapy

Postmastectomy radiotherapy (PMRT) is an integral component of the multimodal treatment of invasive breast cancer in patients with sufficient risk of harboring a reservoir of locoregional disease despite mastectomy and systemic therapy. Microscopic residual disease in the chest wall and/or regional lymph nodes, if left untreated, may seed or reseed distant metastases after initial clearance of distant disease by highly effective contemporary systemic therapies. In addition, occult disease may also serve as a source of locoregional recurrence, which is often highly morbid to the patient in the postmastectomy setting. Therefore, the goal of PMRT is to eliminate residual occult locoregional disease and reduce the risk of both locoregional and distant recurrences. This chapter focuses on the role of PMRT in the treatment of patients with invasive breast cancer and the evidence regarding the impact of PMRT on locoregional control and overall survival. It begins by reviewing the evidence from randomized trials, followed by a discussion of how best to generalize from these trials and select patients appropriately for treatment, especially among those with N1 and N0 disease, for whom treatment is more controversial. It then turns to special considerations, including axillary management postmastectomy in patients with limited volume node-positive disease treated without axillary node dissection, the role of PMRT in patients who were treated with neoadjuvant chemotherapy, implications of differences in tumor biologic subtype, and the optimal integration of PMRT and breast reconstruction.