A recent paper found an increased risk for malignant melanoma in men who took sildenafil (Viagra) for erectile dysfunction.

Unlike some observational studies, this is not being exaggerated by attention-whoring researchers. They are cautious about what it means and doesn't mean. The media is making hay, of course, and they may be making it for good reason.

The prospective cohort study was based on participants in the Health Professionals’ Follow-up Study who were questioned regarding sildenafil use for erectile dysfunction in the year 2000. A total of 25,848 men were used after excluding those who reported cancers at baseline.

By 2010, 142 men had malignant melanoma. Twice as many of the men had taken sildenafil, double the melanoma rate for men who did not. There was no association with squamous cell carcinoma and basal cell carcinoma and men who had erectile dysfunction but did not take sildenafil did not have higher melanoma rates, even though 20X as many men had BCC, so it was a much larger pool.

Why do I say the media may be talking about it for good reason? For starters, they planned the study in advance. We have all seen crazy claims based on weak observational studies that were retrospective - someone wants to blame pesticides for tiny penises and finds data to show it. This was instead planned because of links between phosphodiesterase 5A (PDG5A) inhibitors (like sildenafil) and melanin synthesis. This was not the kind of data dredging we see in too many modern epidemiological studies.

The second reason this may be worth talking about is because the American Council on Science and Health has not clobbered it. In their analysis, they agree with the biologically plausible mechanism and state that it was solidly conducted. Dr. Josh Bloom, ACSH Director of Chemical and Pharmaceutical Sciences, said, “The mechanism that the authors propose is very complicated, but this is to be expected. The processes of cell proliferation and survival are dependent upon a large number of interdependent biochemical events, all falling under the general topic called cell signaling. Although not proven, the proposed role of sildenafil in these processes is reasonable, and this does help support their findings.”

Dr. Bloom also has a column here and, if you have read it, you know he will not be shy to heap scorn on suspect methodologies. There are more PDG5A inhibitors, such as Cialis and Levitra, today than there were in 2000 so follow-up studies could include those and really close in on answers.

Citation: Wen-Qing Li, Abrar A. Qureshi, Kathleen C. Robinson,  Jiali Han, 'Sildenafil Use and Increased Risk of Incident Melanoma in US Men A Prospective Cohort Study', JAMA Intern Med. April 07, 2014. doi:10.1001/jamainternmed.2014.594