ObjectiveTo understand the progress of postmastectomy radiotherapy (PMRT) in patients with T1–2N1M0 breast cancer. MethodThe studies and the treatment guidelines relevant to PMRT in the patients with T1–2N1M0 breast cancer in recent years were analyzed and summarized. ResultsThe ability of PMRT to improve the prognosis of patients with T1–2N1M0 breast cancer remained controversial. Owing to the patients with T1–2N1M0 breast cancer were heterogeneous, and the indications for PMRT had not been standardized. With the increasing use of neoadjuvant chemotherapy for early-stage breast cancer, some studies had attempted to formulate decisions about PMRT based on changes in tumor characteristics before and after neoadjuvant chemotherapy, but the findings were currently controversial. ConclusionsWhether PMRT can improve prognosis and decision-making for patients with T1–2N1M0 breast cancer is still controversial. Some ongoing clinical trials may provide some references for the optimal decision-making of PMRT for patients with T1–2N1M0 breast cancer.