While it is well established that men get cancer more than women, and sometimes at considerably higher rates, few scientists have examined why. In an article published this month in the online version of the European Journal of Epidemiology, a group of American and Swedish researchers, including the Cancer Prevention Institute of California (CPIC), present the results of a worldwide study that found that for 32 out of 35 cancers, men are at higher risk.

For 14 cancers the risk among men is double that of women. And for five cancers ? cancers of the larynx, hypopharynx (the part of the throat that connects to the esophagus), lip, urinary bladder and Kaposi sarcoma ? men have more than four times the risk of women.

Quadrupling the risk
?Differences this large are unusual,? says senior author and CPIC Research Scientist Ellen Chang. ?To give you a sense of how strong male gender is as a risk factor for many of these fourteen cancers, it?s about equivalent to having a first-degree family history of cancer. By quadrupling the risk of five cancers, being male is an exceptionally strong risk factor? it?s like having multiple first-degree relatives with cancer.?

Difference in Cancer risk
In the largest study to date of the gender gap in cancer, scientists from CPIC, the Harvard School of Public Health, and theKarolinska Institute in Stockholm, Sweden, analyzed almost 15 million cases in 60 countries of 35 different types of cancer to understand how men and women differ with respect to cancer risk. The source of this information was the International Agency for Research on Cancer(IARC).

Environmental and behavioral factors
The authors suggest that gender differences in cancer risk for some sites could be explained in part by different exposures to environmental and behavioral factors such as smoking, occupation, and alcohol consumption, but that the majority of the gender gap probably results from key biological factors that differ between all males and females.

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Entirely unexplained
After considering the consistency of the excess cancer risks across different countries and over time, and in view of known risk factors for each cancer type, the authors conclude that for many cancers, the gender gap is ?entirely unexplained.? Therefore, the authors urge further research to understand the biological basis of these remarkable differences. ?If we could find out what causes the male excess of cancer and somehow eliminate it, we could prevent roughly one-third of all cancer,? Chang said. ?Simply being male is responsible for a huge percentage of our worldwide cancer burden.?

For more information:
Edgren G, Liang L, Adami H, Chang ET. Enigmatic sex disparities in cancer incidence. European Journal of Epidemiology DOI: 10.1007/s10654-011-9647-5 Online First?

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