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Most Cancers Strike Men, But Reasons Are Enigmatic.

Article / Review by on February 9, 2012 – 9:30 pmNo Comments

Most Cancers Strike Men, But Reasons Are Enigmatic

It is well known that most cancers strike men more often than women. In many cases these differences can be explained by known risk factors such as smoking, drinking, or occupational hazards. But more than one-third of the cancers that disproportionately strike one sex or the other—men, in particular—cannot be explained by known risk factors and seem to be associated with gender alone, according to research led by Gustaf Edgren, a research fellow in the Department of Epidemiology at Harvard School of Public Health (HSPH).

Most Cancers Strike Men, But Reasons Are Enigmatic

The new study, published online January 13, 2012 in the European Journal of Epidemiology, is the largest to date to examine the disparities in cancer rates between the sexes and what might account for them.

According to the World Health Organization, there were 12.7 million new cancer cases around the world in 2008, with 6.6 million cases occurring in men and 6 million in women. The number 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 some sort of intrinsic, sex-specific biological factors or a difference in susceptibility to risk factors. They add that if the causes of the disparities could be identified—and were modifiable—more than a third of cancers could be prevented.

“Not only do men have an increased risk of 32 of the 35 most common cancers, but, intriguingly, for many of these 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.”

For their analysis, the researchers analyzed almost 15 million cases of cancer in 60 countries, drawing on a worldwide database of cancer statistics, Cancer Incidence in Five Continents.

Cancer strikingly more common in men

The researchers examined two broad questions. Of the 35 types of cancer in the study, they looked at which strike mostly men or mostly women, and quantified the disparity in each case. They also grouped the cancers according to known risk factors, focusing especially on factors that could contribute to gender differences.

Analyzing cancer rates alone, the researchers found that, for nearly half of the 35 cancers examined, men were struck by the disease twice as often as women. For five of the cancers, the male risk was fourfold. Those five cancers included cancers of the larynx, hypopharynx (the  bottom part of the throat), and lip; urinary bladder cancer; and Kaposi sarcoma (a rare form of skin cancer).

Risk factors often unclear

Next, researchers looked at risk factors for the 35 cancers. For 13 types—12 of which strike men more often than women—they found no known risk factors that could plausibly explain the sex disparities. In many cases, those disparities remained consistent over four decades. Some of those cancers included thyroid cancer, myeloid leukemia, multiple myeloma, and non-Hodgkin lymphoma.

View a graph of cancers where the causes of sex differences are unknown.
Cancers where the cause of the sex dierences are still unknown

Thyroid cancer was the only type of the 13 that disproportionately affects women. In fact, for thyroid cancer, sex is the strongest known determinant. Researchers have postulated a link with female sex hormones to explain this disparity, but the evidence is contradictory so there is no consensus on the matter.

“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.”

Further research is needed to determine the causes of the significant sex disparities in cancer rates, said Edgren, adding that he believes the new research “can serve to guide researchers in fruitful directions.”

By Karen Feldscher

photo: Rupak de Chowdhuri/REUTERS

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About Harvard Medical School (HMS)

Driving Change. Building Momentum. Making History.

“Since 1872, Harvard Medical School has been the incubator of bold ideas—a place where extraordinary people advance education, science and health care with unrelenting passion.

Whether training tomorrow’s doctors and scientists, decoding the fundamental nature of life, advancing patient care or improving health delivery systems around the world, we are never at rest. Allied with some of the world’s best hospitals, research institutes and a University synonymous with excellence, the School’s mission remains as ambitious as it is honorable: to alleviate human suffering caused by disease.”

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About Harvard School of Public Health (HSPH)

Harvard School of Public Health is dedicated to advancing the public’s health through learning, discovery and communication. More than 400 faculty members are engaged in teaching and training the 1,000-plus student body in a broad spectrum of disciplines crucial to the health and well being of individuals and populations around the world. Programs and projects range from the molecular biology of AIDS vaccines to the epidemiology of cancer; from risk analysis to violence prevention; from maternal and children’s health to quality of care measurement; from health care management to international health and human rights.

More at Harvard School of Public Health (HSPH) & Harvard School of Public Health (HSPH). History.

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About Harvard University.

Established in 1636, Harvard is the oldest institution of higher education in the United States. The University, which is based in Cambridge and Boston, Massachusetts, has an enrollment of over 20,000 degree candidates, including undergraduate, graduate, and professional students. Harvard has more than 360,000 alumni around the world.

Harvard University is devoted to excellence in teaching, learning, and research, and to developing leaders in many disciplines who make a difference globally. Harvard faculty are engaged with teaching and research to push the boundaries of human knowledge. For students who are excited to investigate the biggest issues of the 21st century, Harvard offers an unparalleled student experience and a generous financial aid program, with over $160 million awarded to more than 60% of our undergraduate students. The University has twelve degree-granting Schools in addition to the Radcliffe Institute for Advanced Study, offering a truly global education.

‘Universities nurture the hopes of the world: in solving challenges that cross borders; in unlocking and harnessing new knowledge; in building cultural and political understanding; and in modeling environments that promote dialogue and debate… The ideal and breadth of liberal education that embraces the humanities and arts as well as the social and natural sciences is at the core of Harvard’s philosophy. ’/ Drew Gilpin Faust

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* The above story is adapted from materials provided by Harvard University

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