Melanoma, Viagra, and PDE5 Inhibitors: Proliferation and Metastasis.

Inhibitors of the cGMP-degrading phosphodiesterase (PDE) 5 have achieved blockbuster status in the treatment of penile erectile dysfunction (PED). Their repurposing is currently being proposed to treat certain solid tumours and various other diseases. In cruel irony, however, it appears from recent clinical studies that PDE5 inhibitors may increase the risk of malignant melanoma by negating newly identified brakes on proliferation and metastasis provided by PDE5A.