Erectile dysfunction drugs and skin cancer — should you worry?

A study published in JAMA Internal Medicine in 2014 found that men who used the erection-enhancing drug sildenafil (Viagra) were 84% more likely to develop melanoma, the most dangerous form of skin cancer, over a period of 10 years.

That finding makes for an attention-grabbing headline. But it's also what I would call a true lie: a scientifically correct statement that could easily be misunderstood to mean "that little blue pill gives you deadly skin cancer."

Here are two truths about this work that you need to know. 1) This study does not show that Viagra causes skin cancer. Instead, it shows that in a large group of men, those who said they used Viagra ended up being diagnosed more often with melanoma than those who didn't use this drug. The study shows a connection, not a cause. 2). Even if Viagra does promote melanoma, the absolute increase is small.

I asked an expert in melanoma and skin cancer risk at Harvard-affiliated Massachusetts General Hospital, Dr. Hensin Tsao, what he thought of the study. He kindly shot back an email offering his perspective: "This is certainly a provocative study and warrants more careful replication. Several factors need to be considered."  Allow me to translate: The devil is in the details. The study is interesting but it does not mean that men should be worried—yet—that Viagra causes melanoma.

But they should definitely be worried about melanoma.

Risky business

The study grew out of laboratory research on how Viagra acts on cell-to-cell signaling pathways. This work demonstrated that the drug mimics key parts of a process that lets melanoma cells spread to other parts of the body. Skin cancer that spreads (metastasizes) is hard to control and can end in death.

To explore whether Viagra might have the same effect on melanoma in humans, a team of researchers looked at data collected from men taking part in the Health Professionals' Follow-up Study, a project based at Harvard that began in 1986. The men filled out health and lifestyle questionnaires every two years. The questionnaire started asking men about use of erectile dysfunction drugs in 2000. In that year, 1,618 men reported having ever used Viagra.

Over the next decade, among the 29,929 men who said they had never used Viagra, 128 developed melanoma. Among the 1,618 Viagra users, 14 developed melanoma. In other words, 4.3 of every 1,000 who didn't take Viagra developed melanoma compared to 8.6 of every 1,000 men who took Viagra.

After statistical adjustments, the increase from 4.3 to 8.6 is the 84% increase in risk that many news reports focused on. Researchers call that the relative risk (one group compared to another). The absolute increase, 4.3 cases per 1,000 men, represents an increase of 0.43%.

Whether a similar connection might exist between other erectile dysfunction drugs and melanoma isn't known. In 2000, when the study was started, Viagra was the only erectile dysfunction drug on the market. Tadalafil (Cialis) and vardenafil (Levitra) weren't approved until 2003, while avanafil (Stendra) came on the market in 2012.

How risky is that business?

The raw numbers suggest that the risk for melanoma associated with Viagra is small—one of the factors that Dr. Tsao said "need to be considered" when weighing the significance of the study. It's even smaller than what was reported in the study because not all of the 14 cancers in the Viagra group can be attributed to the drug. Many factors affect a man's risk of melanoma—the most important of which are age and cumulative exposure to ultraviolet (UV) radiation.

Should you worry?

Should men who use Viagra worry about getting melanoma? Right now, no one can say. The relationship could be pure coincidence. Epidemiological studies like this one tell you only who is at the scene of the crime, not who done it. The findings of the JAMA Internal Medicine study need to be replicated in other groups of men before sounding any warning bells.

In the meantime, Dr. Tsao offers some urgent advice to men: Protect your skin from too much sun and have routine skin checks to identify melanoma and other types of skin cancer early, while they are still treatable.

That's especially important for older men, who are at greater risk for developing melanoma and also at greater risk for 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.

In short, be afraid—but not of Viagra. Be concerned about getting too much sun and pay attention to weird-looking moles that could turn into metastatic cancer. Cover up when you go outside, and use a broad-spectrum sunscreen liberally when you do go out into the sun to work and play.