In conclusion, our study found that the overall recurrence and LRR rates were substantially low in patients with pT1-2N0 breast cancer treated with mastectomy and systemic therapy without PMRT. This finding shows that mastectomy without PMRT is a sufficient local treatment for pT1-2N0M0 breast cancer. However, there was a patient group at high risk for recurrence: the 7-year LRR rate in patients aged ≤ 40 years with T2 tumors was 12.4%, and the 7-year AFR rate of patients with two to three adverse factors, among those aged ≤ 40 years, T2 tumors and the TN subtype, was 15.7%. PMRT might be considered for these high-risk patients.