Men who take once-daily aspirin have nearly double the risk of melanoma compared to men who are not exposed to daily aspirin, reports a new Northwestern Medicine study.

Women, however, do not have an increased risk in this large patient population.

"Given the widespread use of aspirin and the potential clinical impact of the link to melanoma, patients and health care providers need to be aware of the possibility of increased risk for men," said senior study author Dr. Beatrice Nardone, research assistant professor of dermatology at Northwestern University Feinberg School of Medicine.

She suggested increasing patient education about sun exposure, avoiding tanning beds and getting skin checks by a dermatologist, particularly for individuals who are already at high risk for skin cancers.

"This does not mean men should stop aspirin therapy to lower the risk of heart attack," she stressed.

Almost half of people age 65 and over reported taking aspirin daily or every other day, according to a 2005 study.

In 2015, about half of a nationwide survey of U.S. adults reported regular aspirin use.

The study was published in the Journal of the American Academy of Dermatology.

Nardone was surprised at the results because aspirin is reported to reduce risk of gastric, colon, prostate and breast cancer.

And some previous studies have reported a reduced risk in aspirin-exposed men and an increased risk in aspirin-exposed women.

Nardone attributed this to variability of the research methods used in studies that look for associations and risks for cancers.

Among the numerous possibilities, one reason men may be more vulnerable could be related to males (human and animal species) expressing a lower amount of protective enzymes, like superoxide dismutase and catalase, compared to females, Nardone speculated.

"These lower levels of protective enzymes suggest that a higher level of resulting oxidative cellular damage in men might contribute to the possibility of developing melanoma," said Nardone, who is an investigator for the Research on Adverse Drug Events and Reports Program at Northwestern.

The study collected medical record data comprising almost 200,000 patients who were aspirin-exposed or aspirin-unexposed (control group), ages 18-89, with no prior history of melanoma and with a follow-up time of at least five years.

For the aspirin-exposed patient population, the study included only patients who had at least one year of once-daily aspirin exposure at a dose of 81 or 325 mg occurring between January 2005 and December 2006 in order to allow for at least five years of follow-up data to detect if melanoma occurred over time.

Out of a total of 195,140 patients, 1,187 were aspirin exposed.

Of these 1,187 patients, 26 (2.19 percent) (both men and women) had a subsequent diagnosis for melanoma compared to 1,676 (0.86 percent) in aspirin-unexposed (men and women) patients.

When the groups were separated into men and women, men exposed to aspirin had almost twice the risk for diagnosis of melanoma (adjusted relative risk: 1.83) compared to men in the same population who were not exposed to aspirin.

Source: Northwestern University