Postmastectomy radiotherapy indications using pathological prognostic staging in node-positive breast cancer

The role of pathological prognostic staging (PPS) on postmastectomy radiotherapy (PMRT) selection remains unclear. This study aimed to investigate the impact of PPS on PMRT selection in patients with node-positive breast cancer (BC). We included women diagnosed with BC between 2010 and 2015 from the Surveillance, Epidemiology, and End Results database. Chi-square test, operating characteristic curve, and competing-risks analyses with the Fine and Gray model were used for statistical analyses. A total of 14,830 patients were included. Overall, 8,807 (59.4%) patients received PMRT while 6,023 (40.6%) did not. Among them, 11,767 patients (79.3%) had their stage changed, with 1,086 (7.3%) upstaged and 10,681 (72.0%) downstaged. PPS had better prognostic accuracy compared with anatomical staging (AS) (P<0.001). Regarding PPS, PMRT significantly decreased 5-year breast cancer-specific mortality in patients with stage IIIA (14.4% vs. 19.7%, P<0.001), IIIB (19.8% vs. 27.2%, P=0.003), and IIIC (38.5% vs. 45.7%, P=0.049) diseases compared with those of other stages. However, no significant effects were observed in stage IA, IB, IIA, and IIB diseases. Our study highlights significant staging differences between AS and PPS in patients with node-positive BC. The high rate of downstaging observed with PPS suggests its potential to enhance risk stratification and optimize treatment strategies, especially in guiding the appropriate use of PMRT.