Cialis, like Viagra, Could be Linked to the Development of Melanoma

F. A. KelleyDefective Drugs, Pfizer

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Research has linked the popular erectile dysfunction drug Viagra (sildenafil) to an increased risk for melanoma, the deadliest form of skin cancer, and now researchers suggest that the similar Cialis (tadalafil) may also be linked to increased melanoma risk.

Cialis, like Viagra, is a PDE5 inhibitor. PDE5 inhibitors help men with erectile dysfunction by inhibiting the secretion of an enzyme that can prevent erection. Studies published in 2011, 2012 and 2014 found that blocking the enzyme could trigger the creation of melanoma cells. An April 2014 study in JAMA Internal Medicine looked at nearly 26,000 men in the United States who take Viagra and found that the melanoma risk for recent users increased by 84 percent, compared with the risk for nonusers. Pfizer, which makes Viagra, does not list the melanoma risk among possible side effects for the drug. Because this was an observational study, it did not show a definitive cause and effect relationship between Viagra use and melanoma, but it did show a correlation. Even after adjusting for other risk factors for melanoma, the men who had recently used Viagra were twice as likely to develop melanoma.

Cialis, a product of Eli Lilly and Co. and the French pharmaceutical company Sanofi, was not yet on the market at time the study was conducted, so the findings do not include men who used Cialis. However, because Cialis is also a PDE5 inhibitor and is longer acting than Viagra, it may also foster the growth of melanoma. In 2011, the medical journal Cancer Cell alerted Viagra and Cialis users that PDE5 inhibitors could encourage invasive melanoma cells. The Journal of Cell Biochemistry published a study in 2012 that determined PDE5 inhibitors such as Viagra and Cialis could promote melanoma development.

Pfizer already faces lawsuits over Viagra and instances of deadly melanoma. The lawsuits say that PDE5 makers should have warned physicians and men about the possible increased risk of melanoma by those who used these drugs. The lawsuit of a California man diagnosed with melanoma, claims no man “would believe or be expected to know that his use of Viagra would expose him to an increased risk of developing melanoma or exacerbating the growth of melanocytes [skin cancer cells] already present in his body.” The legal complaint says Pfizer “purposefully downplayed, understated and outright ignored the melanoma-related health hazards and risks associated with using Viagra.”

Melanoma is a cancer that starts in the melanocytes, which are the cells that give skin its tan or brown color. Signs of melanoma are usually brown or black spots, but some melanomas can make the skin appear pink, tan or white. Any change in a mole or pigmentation of the skin should be checked by a doctor because melanoma is less likely to spread if caught and treated early. Melanoma is deadly when it spreads to other organs.

The National Cancer Institute (part of the National Institutes of Health) explains that melanoma is more likely than squamous cell carcinoma or basal cell carcinoma to spread to other parts of the body, causing further tissue damage and complicating the possibility for effective treatment and eradication of the cancerous cells.