ABSTRACT
Objective:To analyze locoregional recurrence (LRR) pattern of patients with pT 1-2N 1 breast cancer after modified radical mastectomy, with and without adjuvant radiotherapy (RT). Methods:A total of 5442 eligible patients with breast cancer from 12 Chinese centers were included. The LRR sites and the effect of RT at different sites on recurrence in patients with and without RT were analyzed. The Kaplan-Meier method was used to calculate the cumulative LRR rate, and the difference was compared by the log-rank test.Results:With a median follow-up time of 63.8 months for the entire cohort, 395 patients developed LRR. The chest wall and supraclavicular fossa were the most common LRR sites, regardless of RT or molecular subtypes. The 5-year chest wall recurrence rates for patients with and without chest wall irradiation were 2.5% and 3.8%( P=0.003); the 5-year supraclavicular lymph nodal recurrence rates for patients with and without supraclavicular fossa irradiation were 1.3% and 4.1%( P<0.001); the 5-year axillary recurrence-free rates for patients with and without axillary irradiation were 0.8% and 1.5%( HR=0.31, 95% CI: 0.04-2.23, P=0.219); and the 5-year internal mammary nodal recurrence-free rates for patients with and without internal mammary nodal irradiation were 0.8% and 1.5%( HR=0.45, 95% CI: 0.11-1.90, P=0.268). Conclusions:The chest wall and supraclavicular fossa are the most common LRR sites of patients with pT 1-2N 1 breast cancer after modified radical mastectomy, which is not affected by adjuvant RT or molecular subtypes. The chest wall and supraclavicular fossa irradiation significantly reduce the risk of recurrence in the corresponding area. However, axillary and internal mammary nodal irradiation has no impact on the risk of recurrence in the corresponding area.