from Harvard School of Public Health, February, 2012 Study published online in European Journal of Epidemiology, January, 2012
That most cancers strike men more often than women isn’t news to the medical world. Known risk factors, such as smoking, drinking or occupational hazards may explain some of the gender difference in contracting the disease. But more than one-third of the cancers that disproportionately strike one sex or the other–men, in particular—can’t be explained by known risk factors.
Research leader Gustaf Edgren, a research fellow in the Harvard School of Public Health’s Department of Epidemiology, says the differences seem to be associated with gender alone.
According to the World Health Organization, there were 12.7 million new cancer cases around the world in 2008. 6.6 million occurred in men and 6 million in women. The total number of cases is expected to increase to 21 million by 2030.
Edgren, senior author Ellen Chang of Stanford University Medical School and researchers from the Karolinska Institute in Stockholm postulate that puzzling sex disparities in cancer rates are likely the result of intrinsic, sex-specific biological factors or a difference in susceptibility to risk factors.
They believe that if the causes of the disparities were identified and were modifiable, more than one-third of cancers could be prevented.
For their study, the researchers analyzed almost 15 million cases of cancer in 60 countries from a worldwide database of cancer statistics, Cancer Incidence in Five Continents.
“Not only do men have an increased risk of 32 of the 35 most common cancers, but intriguingly, for many of those cancers the male excess risk is very strong. The risk has remained almost constant since at least the 1960s, and is completely enigmatic,” said Edgren. “We simply have no idea why.”
The research team found that for nearly half of the 35 cancers examined, men contracted the disease twice as often as women. The male risk was fourfold in five of the cancers: cancers of the larynx, hypopharynx, and lip; urinary bladder cancer; and Kaposi sarcoma.
For 13 of the 35 cancers, 12 of which strike men more often than women, they found no known risk factors that could plausibly explain the sex disparities. Those disparities remained consistent over four decades. Some of the cancers included thyroid cancer, myeloid leukemia, multiple myeloma and non-Hodgkin lymphoma.
“While the sex disparity for most of these cancers is fairly well-known, no one has really taken a holistic view of this topic before,” Edgren said. “Both within science and outside, I’ve yet to come across anyone who is aware of just how large these differences are. Here we show that cancer is first and foremost a disease of men.”