The US Food and Drug Administration (FDA) said it will study a potential link between melanoma and erectile dysfunction (ED) drugs such as sildenafil (Viagra, Pfizer) and tadalafil (Cialis, Lilly), a trail other researchers have gone down only to turn up less-than-conclusive results.
The announcement appeared in the agency's latest watch list of drugs with possible safety issues collected by the FDA Adverse Event Reporting System (FAERS) in the first 3 months of 2016. In all, the watch list contains 17 drugs or drug classes, including treatments for cancer, circulatory problems, psychiatric conditions, and diabetes. Regarding that last disease, the agency said it was checking out patients experiencing hepatitis after taking drugs that contain metformin.
The agency will be on the heels of other researchers when it comes to the class of ED drugs called phosphodiesterase (PDE)-5 inhibitors. A study published in JAMA Internal Medicine in April 2014 found an association between sildenafil and an increased risk for melanoma. However, the authors said their epidemiological evidence was not strong enough to change clinical recommendations for treating ED.
Likewise, a study published in JAMA in June 2015 did not nail down a cancer risk for these drugs. Mining a massive health database of Swedish patients, the authors reported that among 4000 men diagnosed with malignant melanoma, use of a PDE-5 inhibitor was linked to a 20% increase in the relative risk for the cancer.
However, one telltale finding weakened this link: The melanoma risk was highest for men who filled only a single prescription for a PDE-5 inhibitor, not for men who filled multiple prescriptions. That counterintuitive fact made the authors suspect that the higher risk had to do with lifestyle or demographic factors. After all, the melanoma risk also was higher for men with more education and income, as well as men with basal cell carcinoma, which was not biochemically implicated with ED drugs. The conclusion? Men taking ED drugs who had melanoma probably were the sort with enough leisure time on their hands to get too much sun exposure.
What the FDA discovers about ED drugs and melanoma remains to be seen.