The study suggests underlying sex differences play a bigger role.
“We were a little surprised that for many cancers these lifestyle factors explained such a small part of the difference,” lead study author Sarah Jackson, PhD, a research fellow in the Division of Cancer Epidemiology and Genetics at the National Cancer Institute, told Verywell via email.
But nobody is surprised that these sex differences exist.
“We’ve always known, ever since we started having registries, which goes back about 120 years now,” Otis Brawley, MD, MACP, professor of oncology at the Johns Hopkins University School of Medicine, told Verywell.
How Much More Likely Are Men to Get Cancer?
Researchers at the National Cancer Institute looked at data on cancer incidence for 21 different types of cancer in organs that both men and women have. The participants were part of the National Institutes of Health-AARP Diet and Health Study which ran from 1995 to 2011.
Among the 171,274 men and 122,826 women between the ages 50 and 71 enrolled in the study, 17,951 new cancers arose in men and 8,742 in women.
The study authors were able to quantify just how much higher the incidence of a few specific cancers were in men:
Esophageal adenocarcinoma: 10. 8x higher in menLaryngeal cancer: 3. 5x higher in menGastric cardia cancer: 3. 5x higher in menBladder cancer: 3. 3x higher in men
Rates of cancers of the liver, biliary tract, skin, colon, rectum, and lung were also higher in men.
Of the organs studied, only the thyroid and gallbladder showed higher cancer rates among women.
What Causes the Difference?
The reasons why men are more likely to develop cancer in most body parts are largely unexplained, the researchers noted. Factors such as sex-related biological mechanisms may play a role, as can immunologic and genetic differences.
Lower levels of estrogen and progesterone in men, which may lower risk of some cancers, could play a role. Higher levels of testosterone levels, which promote cell growth, may also make a difference.
Jackson and Brawley each highlighted the impact of X and Y chromosomes.
“The X chromosome contains several tumor suppressor genes,” Jackson said. “Because they have two X chromosomes, females may have higher expression levels of these genes than males, who only have one.”
Even body size matters, she added.
“Height has been associated with increase risk of a few cancers,” Jackson said. “This may be because taller people have more cells than shorter people, or it could be that height is a marker for growth hormone levels.”
Every human being develops mutations on a daily basis that can lead to cancer; the body has ways of killing these cancerous cells or stopping their growth, Brawley said. But larger people have more cells that could potentially become cancerous.
“The more cells you have, the more cells that are going to be in mutation, with a chance for aberration on a daily basis,” he said.
Larger people, especially those who are overweight or prediabetic, have more circulating insulin, Brawley added. Insulin can promote the growth of blood vessels that a tumor needs to grow.
What Can We Do With This Information?
A better understanding of why sex differences in cancer rates exist can help lead to new treatments, Jackson said.
“If we can discover the mechanisms by which females have an immune advantage, we may be able to develop therapeutics to bolster the immune system to prevent and treat cancer,” she said. “It’s important for researchers to report findings on cancer incidence, screening, and survival by sex to ensure that we are not missing important sex-specific associations.”
