Men's higher risk of most cancers may be due to biological, not lifestyle, differences

Aug. 8 (UPI) -- It's been unclear why men face a higher risk of cancer than women at most shared anatomical sites. But a new study suggests the cause may be underlying biological differences, not lifestyle behaviors such as smoking, alcohol use and diet.

In fact, men have an increased risk of most cancers even after adjusting for a wide range of risk behaviors and carcinogenic exposures, according to research led by the National Cancer Institute, part of the National Institutes of Health.

The study's findings were published Monday in Cancer, a journal of the American Cancer Society.

"Our results show that there are differences in cancer incidence that are not explained by environmental exposures alone. This suggests that there are intrinsic biological differences between men and women that affect susceptibility to cancer," Sarah S. Jackson, the study's corresponding author, said in a news release.

Understanding the reasons for sex differences in cancer risk could provide important information to improve prevention and treatment, added Jackson, research fellow in the National Cancer Institute's Division of Cancer Epidemiology and Genetics.

In the study, the researchers quantified the extent to which behaviors such as smoking and alcohol use; anthropometrics, including body mass index and height; lifestyle factors, such as physical activity, diet and medications, along with medical history collectively explain the male predominance of risk at 21 shared cancer sites.

Their analysis included 171,274 male and122,826 female participants, ranging in age from 50 to 71 years old, in the National Institutes of Health-AARP Diet and Health Study that ran from 1995 to 2011.

Of 26,693 cancers found -- 17,951 in men and 8,742 in women, the incidence was significantly lower in men than in women only for thyroid and gallbladder cancers, the researchers said. Risks were 1.3 to 10.8 times higher in men than women at other anatomic sites.

The greatest increased risks in men were seen for esophageal cancer, at a 10.8 times higher risk; larynx, at 3.5 times higher risk; gastric cardia, at 3.5 times higher risk, and bladder cancer, at 3.3-times higher risk, according to the research paper.

Differences in risk behaviors and carcinogenic exposures between the sexes only accounted for a modest proportion of the male predominance of most cancers, ranging from 11% for esophageal cancer to 50% for lung cancer, the researchers said.

In an accompanying editorial, public health researchers at Washington University School of Medicine in St. Louis said the best strategy is to include sex as a biological variable along the whole cancer continuum, from risk prediction and prevention to screening and treatment.

They pointed out limitations of the study, including not taking into account death from causes other than cancer in elderly populations, not accounting for some important cardiovascular risk factors for which men are known to be at higher risk, and collecting data mostly on the White population.

Jingqin Luo, a co-author of the editorial, told UPI in an email that non-genetic risk factors explained less than half of men's higher cancer rates. And, she said, sex disparities in cancer incidence are due to the interplay of many risk factors: "genetic, epigenetic, non-genetic lifestyle and social determinants of health."

Further research is needed to better understand this interplay of risk factors, she said.

In the meantime, two lifestyle factors -- smoking and drinking -- are found to contribute to nearly all of the 21 cancer types, said Luo, associate professor of surgery in the Washington University School of Medicine's Division of Public Health Sciences.

"Thus, behaviors still make a difference in cancer risk," she said. "The modifiable nature of behavior/lifestyle factors makes them ideal means for cancer prevention and intervention."