Women show survival advantage over men for 13 cancers: StatsCan

Canadian women show a survival advantage over men for 13 of 18 cancers, excluding sex-specific ones, according to Statistics Canada, but the reasons aren't well understood.

Larry Ellison of the agency's health statistics division analyzed data from the Canadian Cancer Registry and a database of vital statistics to compare cancer survival based on the relative excess risk of death from the disease among women and men diagnosed with all cancers combined and 18 individual malignancies.

Overall, there was a 13 per cent lower excess risk of death among women younger than 55 for all cancers combined, Ellison said in Wednesday's issue of Health Reports.

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Cancers of the genital system and breast cancers were excluded. Ellison took age into account. For all cancers combined, he also adjusted for the case mix or chance that women were diagnosed more often with cancers with a better prognosis.

The results were roughly similar to what has been found in the United States and Europe, he said.

"It is very interesting to see this data, what it is in Canada," Ellison said in an interview.

The study describes what is happening. It doesn't analyze the reasons why. 

Other researchers have postulated why, Ellison said, suggesting that female hormones may offer a protective effect before age 55, which he chose as a rough proxy for age of menopause.

"We find a 23 per cent lower risk of excess risk of death risk in the 15 to 55 category so that lends indirect support to that theory that's been postulated but it doesn't prove. Nothing direct would go along with it."

The advantage was greatest for thyroid cancer, skin melanoma and Hodgkin's lymphoma, followed by oral cancer, lung cancer, non-Hodgkin's lymphoma, and brain and other nervous system cancers.

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The Canadian Cancer Society's annual statistics also show women are at a survival advantage for the three cancers with the greatest survival differences, said Robert Nuttall, assistant director for health policy at the Canadian Cancer Society in Toronto.

"I think that knowing it's not just those three but there's 13 different cancer types that women survive better, and in fact there's only one cancer type that men have better survival rates, I think that's quite surprising," Nuttall said.

Bladder cancer was unique. It was the only cancer for which women were at a survival disadvantage.

In general, many explanations are possible, Ellison said. He suggested the research community could take the information to study individual cancers in more detail as well as to try to understand the results in a global context.

"It tells us we need to look at the way we look at health and the way we approach health-care delivery differently to make sure that survival rates do improve. In the case of men versus women, it can influence the way we encourage men to do adopt healthier behaviours or to seek out medical attention earlier," Nuttall said. 

Knowing where there are differences can help inform some treatment decisions and followup support services for cancer, he said.

The cancers were diagnosed from 1992 to 2009 and the mortality was followed until the end of 2008.