Comparative Net Survival Analysis of Men and Women With Breast Cancer in Japan: A Population-Based Study.

While male breast cancer (MBC) remains a rare and understudied disease, comparatively little is known about its prognosis in contrast to female breast cancer (FBC). There is a paucity of large population-based studies comparing the prognosis of MBC patients to FBC patients in Japan. This study analyzed 181,540 breast cancer cases, 1058 (0.6%) males and 180,482 (99.4%) females, from 12 prefectures in Japan diagnosed between 1993 and 2011. Five- and ten-year net survival (NS) were estimated and stratified by sex, period, age, stage, and histological groups. Excess hazard ratios (EHR) were adjusted for period, age, stage, and histological group. Cochran's Q test was utilized to assess heterogeneity across these factors. The overall 5- and 10-year NS estimates for MBC patients were 90.7% (95% CI: 86.3%-93.7%) and 83.7% (95% CI: 72.2%-90.8%), respectively, while those for FBC patients were 88.3% (95% CI: 88.1%-88.5%) and 79.1% (95% CI: 78.7%-79.4%), respectively. The survival of MBC patients was comparable to that of FBC patients, with EHR of 0.88 [95% CI: 0.70-1.09] and 0.86 [95% CI: 0.69-1.07] for 5- and 10-year survival, respectively. Heterogeneity analysis revealed no significant sex-based differences in survival across these strata. This study offers a comprehensive analysis of breast cancer survival in Japanese men and women and enhances understanding of MBC prognosis relative to FBC.