A prostate cancer breakthrough could stop the tumor spreading after it becomes resistant to current therapy, scientists say.

Anti-hormonal treatment blocks the signal sent out by testosterone that stimulates tumor growth.

But eventually the cancer cells become resistant and the growth spreads through the body becoming fatal.

An international research team led by Dutch scientists found proteins that normally regulate the circadian rhythm, or body clock, dampen the effects of the anti-hormonal therapy.

The breakthrough means current drugs could be repurposed and has saved a decade of testing.

The exact process of how tumor cells become resistant to hormone therapy had been a mystery until now.

For the study, the team looked at tissue from 56 people with high-risk prostate cancer who had undergone three months of anti-hormonal therapy before their surgery.

The team examined the tissue at DNA level after the three months were up.

Genes keeping the cells alive despite the treatment were controlled by a protein that normally regulates the body clock.

This protein was found to make prostate cancer cells more sensitive to anti-hormonal therapy in the lab as well as in mice.

The researchers say there is no evidence to suggest people with out of kilter body clocks, such as night shift workers, could be at a higher risk from the disease.

"Prostate cancer cells no longer have a circadian rhythm," lead researcher Dr Wilbert Zwart from the Netherlands Cancer Institute said. "These ‘circadian clock' proteins acquire an entirely new function in the tumour cells upon hormonal therapy.

"They keep these cancer cells alive, despite treatment. This has never been seen before.

"Our discovery has shown us that we will need to start thinking outside the box when it comes to new drugs to treat prostate cancer and test medicines that affect the circadian clock proteins in order to increase sensitivity to hormonal therapy in prostate cancer.

"Fortunately, there are already several therapies that affect circadian proteins, and those can be combined with anti-hormonal therapies.

"This lead, which allows for a form of drug repurposing, could save a decade of research."

The findings were published in Cancer Discovery, a journal of the American Association for Cancer Research.

Featured image: Netherlands Cancer Institute

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