Postmastectomy radiotherapy benefit in Chinese breast cancer patients with T1-T2 tumor and 1-3 positive axillary lymph nodes by molecular subtypes: an analysis of 1369 cases.

The aim of this study was to examine the association between molecular subtype (MST) and prognosis and research the postmastectomy radiotherapy (PMRT) effect in T1-T2 tumors with 1-3 positive axillary lymph nodes (ALNs). This retrospective study studied breast cancer patients with T1-T2 tumors and 1-3 positive ALNs according to MST: Luminal A, Luminal B, human epidermal growth factor receptor-2 (Her-2) positive, and Triple negative. The impact of adjuvant PMRT in T1-T2 tumors with 1-3 positive ALNs was also assessed. This study included 1369 patients: 33.0 % Luminal A, 42.9 % Luminal B, 11.9 % Her-2 positive, and 12.2 % Triple negative. On univariate and multivariate analyses, MST was associated with locoregional relapse (LRR). Kaplan-Meier analysis showed that PMRT significantly decreased LRR risk (p = 0.017) and distant metastasis (DM) risk (p < 0.0001). In subgroup analysis, PMRT showed significant benefits of improvement in LRR in patients with younger age, positive lymphovascular invasion (LVI), and ratio of positive lymph nodes (LNs) >25 %. Moreover, the nomogram could more accurately predict LRR (c-index 0.75) in T1-2N1 breast cancer patients. MST associated with patient outcomes in breast cancer patients with T1-T2 tumors and 1-3 positive ALN. It makes sense to offer PMRT for patients aged<40 years old, LVI, 2 and 3 positive lymph nodes, and ratio of positive LNs >25 %.