Gender differences in stomach cancer survival in Osaka, Japan: analyses using relative survival model

Relative 5-year survival for stomach cancer has increased gradually in Osaka for more than two decades, while women show a small but consistently lower survival for it. We analyzed gender differences in stomach cancer survival, using relative survival model proposed by Dickman et al. Study subjects were reported stomach cancer cases diagnosed in 1975-99. We estimated the excess hazard ratios (EHRs) of death using Poisson's regression model. The crude EHR for women was 1.12 [95% confidence interval (CI): 1.09-1.14] in comparison with men. After adjustments for year and age at diagnosis, the EHR for women decreased to 1.07 (95% CI: 1.05-1.09), and furthermore, it reached to an insignificant level of 1.02 (95% CI: 0.99-1.04) after an additional adjustment for the extent of disease (localized, regional, distant and unknown). With further adjustments by histological type (intestinal, diffuse and others/unknown), method of detection (screening or not) and treatment (surgery or not), the EHR decreased to 0.97 (95% CI: 0.94-0.99), significantly lower than the unity. These results indicate that the lower stomach cancer survival among women was attributable mainly to more advanced stages among women. The survival for women would have been a little better than for men if prognostic factors for stomach cancer had been comparable between the sexes. Inequality by the gender in taking screening, medical examination or treatment for stomach cancer was suggested to exist in Osaka, Japan.