Abstract
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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
Findings
Studies in Europe, the United States, and Korea have recently reported that women have an advantage over men in surviving a diagnosis of cancer. A biological advantage mediated through sex hormones has been proposed. Another possibility is that the difference may, in part, reflect women’s generally healthier attitudes and behaviours. Whether the explanation is biological or cultural, or a combination of the two, has yet to be determined. Analyses of data from population-based cancer registries may be used to reduce, or at least better understand, sex-specific disparities in cancer prognosis. [Full Text]
Authors
Larry F. Ellison (larry.ellison@canada.ca) is with the Health Statistics Division at Statistics Canada, Ottawa, Ontario.
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What is already known on this subject?
- In Europe and the United States, women have recently been described as having an advantage over men in surviving a diagnosis of cancer.
- Women’s survival advantage is more pronounced when cancer is diagnosed before age 55.
- Differences in cancer prognosis by sex have not been systematically studied in Canada.
What does this study add?
- The prognosis after a diagnosis of cancer among Canadian residents was significantly better for women than men for a majority of individual cancers, and for all cancers combined.
- For the cancers studied, women’s advantage was almost uniformly greater among those diagnosed at younger ages (15 to 54).
- Women’s advantage was greatest for thyroid cancer, skin melanoma and Hodgkin lymphoma.
- The relatively large advantage for women diagnosed with thyroid cancer was somewhat attenuated, though still significant, in earlier time periods when the rate of diagnosis of this cancer was lower.
- A significant disadvantage for women emerged only for bladder cancer; the excess risk for women seemed to be restricted to the first 12 to 18 months after diagnosis.
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