A single protein molecule seems to be the source of hormone therapy-resistant prostate cancer and its discovery has increased the confidence among scientists this aggressive form of cancer might yet be mitigated.

The discovery of the molecule, GPR158, means drugs that prevent the development of treatment-resistant prostate cancer are bound to be developed. GPR158 is linked to a biological process that plays a key role in the way prostate cancer stops responding to standard hormone therapies.

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Prostate cancer initially responds to drugs that prevent male hormones fueling tumor growth. The cancer, however, eventually becomes resistant to hormonal treatment. It then progress quickly and death is often close behind.

Scientists believe GPR158 will be targeted by new prostate cancer drugs. Patients with high levels of this protein are more likely to experience a recurrence of prostate cancer.

It was discovered by accident by researchers searching for new drug targets for glaucoma, an eye disease.

When a prostate cancer tumor is in its early stages, it depends on hormones called androgens to grow. Eventually it progresses to a more lethal form, called castration-resistant prostate cancer (CRPC), and is resistant to drugs that block androgen receptors, said lead scientist Dr. Nitin Patel from the University of Southern California.

"We found that GPR158, unlike other members of the GPCR family, is stimulated by androgens, which in turn stimulates androgen receptor expression, leading to tumor growth".

The team also discovered that GPR158 is associated with a process called neuroendocrine transdifferentiation that plays a crucial role in the development of hormone therapy-resistant cancer.

Dr Matthew Hobbs, deputy director of research at Prostate Cancer UK, said figuring out why prostate cancer stops responding to treatment over time is one of the big unanswered questions.

He said finding these answers could hold the key to developing new treatments to save thousands of men dying from prostate cancer every year.