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

Background: 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).

Methods: 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.

Results: 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.

Conclusions: 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.