Is post-mastectomy radiation required in patients with cT2N1 breast cancer who undergo neoadjuvant chemotherapy and are then found to have negative lymph nodes at the time of mastectomy?

This particular subset of patients has the most data suggesting that response to neoadjuvant chemotherapy can be used to tailor post-mastectomy radiation (PMRT) decisions. A retrospective study from MD Anderson (McGuire IJROBP 2007) evaluated 106 patients who received neoadjuvant chemotherapy and achieved a pathologic complete response in the breast and axilla at the time of mastectomy; 72 had PMRT and 34 did not. In the subset of patients with stage II disease, there were no locoregional recurrences (LRR) in either group, suggesting it may be reasonable to omit PMRT in this setting. Additionally, more recent data from the pooled analysis of NSABP studies B-18 and B-27 (Mamounas JCO 2012) showed low rates of LRR in patients with tumors <5 c...