Differences in cancer survival in Canada by sex

Abstract

Background: Research in the United States and Europe has found that women have an advantage over men in surviving a diagnosis of cancer, but the issue has not been systematically studied in Canada.

Data and methods: Data are from the Canadian Cancer Registry, with mortality follow-up through record linkage to the Canadian Vital Statistics Death Database. The percentage unit difference in five-year relative survival ratios (RSRs) between women and men and the relative excess risk (RER) of death for women compared with men were used as measures of differences in cancer survival.

Results: A significant advantage for women compared with men was observed in 13 of the 18 cancers studied. Point estimates of RER were almost uniformly lower among those diagnosed at younger ages (15 to 54). For all cancers combined, women had a 13% lower excess risk of death-23% lower among women younger than 55. The overall advantage was greatest for thyroid cancer (RER = 0.31), skin melanoma (0.52) and Hodgkin lymphoma (0.65). The advantage for thyroid cancer was somewhat attenuated, though still significant, in earlier time periods. Bladder cancer was the only cancer for which women had a significant disadvantage (RER = 1.23); this excess risk seemed to be restricted to the first 12 to 18 months after diagnosis.

Interpretation: The reasons behind sex-specific differences in cancer survival are not well understood. Many explanations are possible, and differences are best explored on a cancer-by-cancer basis. The pronounced advantage for women at younger ages lends indirect support to a hypothesized hormonal influence.

Keywords: Excess risk; gender differences; neoplasms; population-based; registries; relative survival; sex hormones; survival analysis.