Men are known to be more likely to develop cancer than women, and a new study suggests that this is largely due to biologic differences between the sexes.
“After controlling for factors like smoking, alcohol use, diet, physical activity and common medical conditions [that increase cancer risk], the sex bias remained for most cancers,” said study author Sarah Jackson, a research fellow at the National Cancer Institute's Division of Cancer Epidemiology and Genetics.
Exactly which biological differences are driving these disparities isn't fully understood yet.
"We'd… like to explore the contribution of sex hormones and genetics to cancer incidence in future research,” she said.
For the study, researchers looked at differences in risk for 21 cancer sites among 171,000 men and 123,000 women between 50 and 71 years of age who were enrolled in a diet and health study from 1995 to 2011.
During that time, 17,951 new cancers were diagnosed in men, and 8,742 were found in women.
Men had higher risks for most cancers, with the greatest difference in risk seen for cancers of the esophagus (10.8 times higher); larynx and bladder (each 3.5 times higher); as well as gastric cardia, a type of stomach cancer (3.3 times higher).
Men only had lower rates of thyroid and gallbladder cancers, the study showed.
Jackson said men are also more likely to die of cancer than women.
Risk factors such as smoking, alcohol, diet and underlying health issues accounted only for a small fraction of the difference in men's and women's cancer rates. For example, smoking, diet and conditions like diabetes that can increase the risk for some cancers explained only 20% of the male bias in bladder cancer. Men are more than three times as likely to develop bladder cancer than women, Jackson said.
The study was published Aug. 8 in the journal Cancer. Going forward, researchers plan to look at sex differences in cancer rates among racial and ethnic groups.
In an editorial that accompanied the findings, Jangqin Luo said more research is needed to understand why men are more likely than women to develop many cancers.
“Sex disparities have been actively studied in the past decades, and the published research findings have deepened our understanding, [but] sex difference in cancer is still an ongoing quest,” said Luo, an associate professor of surgery at the Washington University School of Medicine in St Louis.
Understanding these disparities will pave the way toward better prevention and treatment policies, she said.
Dr. Otis Brawley, a professor of oncology at Johns Hopkins University School of Medicine in Baltimore, agreed that it's time to pay more attention to sex differences in cancer rates.
“The more cells you have, the more likely one of them is to become malignant, and men tend to be bigger than women,” said Brawley, who reviewed the findings.
Some of these differences may be related to hormones. The male sex hormone testosterone may promote the growth of some cancers, and the female sex hormone estrogen may offer protection against others.
“When we do epidemiological studies and treatment studies, it is important to look at men versus women,” Brawley said.
Eating a healthy diet, maintaining a normal weight, not smoking or drinking alcohol in excess, and other healthy behaviors are still an important part of a cancer prevention strategy for men and women, he said.
The U.S. Centers for Disease Control and Prevention offers more information on how to prevent cancer.
SOURCES: Sarah Jackson, PhD, MPH, research fellow, National Cancer Institute, Rockville, Md.; Jangqin Luo, PhD, associate professor, surgery, Division of Public Health Sciences, Washington University School of Medicine, St. Louis; Otis Brawley, MD, professor, oncology, Johns Hopkins University School of Medicine, Baltimore; Cancer, Aug. 8, 2022