[Risk-adapted postmastectomy radiotherapy based on local-regional recurrence for T1-2N1M0 breast Cancer]

Objective: To establish a risk-adapted postmastectomy radiotherapy strategy based on local-regional recurrence for intermediate-risk breast cancer (T1~2N1M0 stage). Methods: A total of 2413 patients with T1-2N1M0 breast cancer were retrospectively reviewed. Of them, 588 patients (24.4%) received postmastectomy radiotherapy (PMRT), while 1 825 (75.6%) patients did not. A comprehensive comparative study was performed by using multivariable and propensity score-matched (PSM) analyses. Results: The median follow-up time was 67.0 months, the 5-year local region recurrence free-survival (LRRFS), disease-free survival (DFS) and overall survival (OS) were 93.8%, 85.7% and 93.3%, respectively. The 5-year local region recurrence (LRR) was 6.1%. For patients without PMRT, multivariable analysis indicated that age, tumor localization, molecular subtype, pathologic T stage and number of positive lymph node were independent factors for LRRFS (all of P<0.05). Patients with T1-2N1 breast cancer were classified into low-risk group (0-1 risk factor, 768 patients), intermediate-risk group (2 risk factors, 690 patients) and high-risk groups (≥3 risk factors, 544 patients) based on the five independent factors mentioned above. The 5-year LRRFS, DFS and OS were significantly different among the three groups (P<0.001). In low- and intermediate-risk groups, there were no significant differences in LRRFS, DFS and OS of patients who received PMRT or not (P>0.05). In high-risk group, the DFS of patients received PMRT or not were 79.8% and 74.4%, respectively (P=0.127), the OS of them were 86.8% and 87.1%, respectively (P=0.174), and the LRRFS were 93.3% and 84.3%, respectively (P=0.002). After PSM adjustment, no significant differences in LRRFS, DFS and OS were observed between PMRT-received subgroup and no PMRT subgroup of low-risk group (P>0.05). In intermediate-risk group, the LRRFS of patients received PMRT or not were 95.2% and 91.0%, respectively (P=0.037). However, in the high-risk group, the LRRFS, DFS and OS of patients received PMRT were 93.3%, 79.7% and 86.6%, respectively, while those of patients did not receive PMRT were 78.5% (P<0.001), 69.5% (P=0.038) and 85.7% (P=0.080), respectively. Conclusions: The local-regional recurrence risks of patients with pT1-2N1 breast cancer are viable and risk-adapted PMRT is available for them. Better prognoses can be achieved by the patients of intermediate and high-risk group. More samples on this subject are needed to validate the results.