In the one more thing to worry about category comes a surprise from a multi-center study just published in JAMA, which postulates that the use of sildenafil (Viagra) may increase the risk of malignant melanoma.
Unlike many of the junk studies we routinely lambaste here, this one is well run and also has a biologically plausible mechanism to explain the findings. It is also a prospective study one planned in advance to explore a theory rather than a retrospective study, (often called data dredging) where data from past studies are analyzed to find some kind of correlation between two events. The former is almost always more scientifically valid compared to the latter.
Lead author Wen-Qing Li, PhD of the Department of Dermatology, Brigham and Women's Hospital at Harvard Medical School and co-workers studied almost 26,000 men over a ten year period. During this time, 142 cases of malignant melanoma were confirmed. Men who had taken sildenafil were found to have twice the incidence of melanoma than those who did not.
As a control, men who had erectile dysfunction (ED) but did not take sildenafil showed no increase, ruling out the possibility that ED itself was a risk factor for higher rates of melanoma.
The possibility that other underlying medical conditions may have played a contributing factor was also controlled for. When men with chronic diseases were excluded from the analysis, there was no change in the incidence of melanoma.
Interestingly, the use of sildenafil was not associated with basal cell carcinoma or squamous cell carcinoma of the skin both slower growing and much less invasive cancers.
The authors conclude: Sildenafil use may be associated with an increased risk of developing melanoma. Although this study is insufficient to alter clinical recommendations, we support a need for continued investigation of this association.
ACSH s Dr. Josh Bloom says, 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 signalling. Although not proven, the proposed role of sildenafil in these processes is reasonable, and this does help support their findings.
He adds, There is a bit of irony here. Viagra was discovered by accident. It was originally intended to be a heart drug, and failed. But, when patients in the clinical trials reported a side effect of erections, someone at Pfizer paid attention and all of a sudden there was a new drug for an unmet medical need. The fact that it may also promote cancer underscores the surprises that you routinely encounter in drug discovery.