Men who take the erectile dysfunction medication Viagra (sildenafil) are 84 percent more likely to develop deadly melanoma skin cancer, according to the results of a study of some 26,000 men.

The study results were reported in the Journal of American Medical Association: Internal Medicine in the spring of 2014.

“Viagra may increase the risk of melanoma because it affects the same genetic pathway that allows the skin cancer to become more invasive,” Dr. Abrar Qureshi, professor and chair of the dermatology department in the Warren Alpert Medical School at Brown University, told NBC News.

“Those who took the drug weren’t at higher risk of other, less-dangerous skin cancers, such as basal cell or squamous cell cancers,” Qureshi explained.

Qureshi was one of several doctors in the United States and China who analyzed data in the long-term study looking at a possible link between Viagra and melanoma skin cancer. The test group involved male doctors and healthcare workers with an average age of 65, 6 percent of whom took Viagra to treat sexual dysfunction.

The risk of developing melanoma skin cancer doubled for men who took Viagra compared with those who never used it.

“That finding held true even when the researchers adjusted for a family history of skin cancer, ultraviolet light exposure in the states where the men lived, other kinds of cancer and major illnesses and other factors,” NBC News reported.

Melanoma skin cancer, according to Skincare.org is the most dangerous type of cancers of the skin.

“Cancerous growths develop when unrepaired DNA damage to skin cells (most often caused by ultraviolet radiation from sunshine or tanning beds) triggers mutations (genetic defects) that lead the skin cells to multiply rapidly and form malignant tumors. These tumors originate in the pigment-producing melanocytes in the basal layer of the epidermis,” the website explains.

“Melanomas often resemble moles; some develop from moles. The majority of melanomas are black or brown, but they can also be skin-colored, pink, red, purple, blue or white. Melanoma is caused mainly by intense, occasional UV exposure (frequently leading to sunburn), especially in those who are genetically predisposed to the disease. Melanoma kills an estimated 9,710 people in the U.S. annually.”

Detected early, melanoma is highly treatable but if left unchecked, it is deadly.

The American Cancer Society estimates that more than 120,000 new cases of melanoma are diagnosed in the United States every year.

Doctors treating older men who use Viagra should regularly check for signs of skin cancer, according to Dr. June Robinson of Northwestern University’s Feinberg School of Medicine.

Melanoma expert Dr. Hensin Tsao of Massachusetts General Hospital told a Harvard health publication that older men are already at a greater risk for developing melanoma and from dying from it.

“An estimated 76,000 Americans (more than half of them men) will be diagnosed with melanoma this year, and almost 10,000 will die from it,”

Despite the large study’s findings, Robinson told NBC News “that the results should be taken with a grain of salt.”

“Its role in the biological behavior of melanoma in older men warrants further study,” she said.