Viagra cancer threat: Erectile drug sildenafil may stimulate skin cancer growth

Taking erectile drug sildenafil, better known as Viagra, may boost the growth of skin tumours, scientists have said. The drug manufactured by Pfizer could indeed have a stimulating effect on the cGMP molecule, which plays a crucial role in the body's cell growth processes.

Researchers from Tübingen University, Germany, believe this interference between Viagra and the molecule can result in the growth of existing malignant skin tumours, or melanomas.

Lead author Robert Feil said that men who suffer from erectile dysfunction should not stop taking the drug. Their study, published in Cell Reports, has only looked at the effect of Viagra in skin tumours in animal models and cell cultures, so they say more clinical research is needed before they can come up with a firm conclusion.

Boosting tumour growth

cGMP is a signalling molecule, with a key function in many different metabolic pathways and thus necessary for the body to work properly. However, researchers have found that cancerous melanomas also use the molecule to spread. An enzyme called PDE5 usually slows down the action of cGMP, but Viagra inhibits this enzyme, essentially allowing the molecule to boost tumour growth.

"PDE5 is like a brake on cGMP," say Feil. "Taking sildenafil basically disables this brake. As a result, the melanoma begins to grow more vigorously."

No new cancers

It is not the first time studies have shown a link between Viagra and the development of cancer. In 2014, American research on 15,000 men revealed sildenafil was connected to a higher risk of malignant melanoma.

The correlation was confirmed by other studies, including one with 24,000 Swedish men. It is the first time however that the scientists tried to explain this association by looking at actual biochemical mechanisms that can occur in the body.

The good news is that the scientists believe the erectile drug does not cause new cancers. It may only act on existing cancerous tumours.

"We are assuming that sildenafil and possibly other PDE5 inhibitors could first and foremost reinforce the growth of existing melanomas – particularly if these medications are taken frequently and in high dosages," says Feil.

Data from the Health and Social Care Information Centre suggest that 1.7 million prescriptions were given for Sildenafil, in 2014, up from 1.4m the year before. With only one million prescriptions in 2004, this amount has almost doubled in ten years.