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 %.