'Exciting' results in prostate cancer drug trial

A new prostate cancer drug for late-stage patients with few treatment options has yielded early trial results described as “extremely exciting”.

Half the men taking the drug abiraterone experienced a substantial drop in blood levels of PSA (prostate specific antigen), the biomarker used to track prostate cancer.

The 47 men recruited for the Phase II trial in the UK and US all had late-stage cancers that were resistant to traditional hormone treatments. In almost every case, the cancer had spread to the bones.

All had received docetaxel, the only currently approved chemotherapy drug known to benefit patients with advanced prostate cancer.

“Docetaxel is an important drug but it extends life for an average of just two to three months, so there is a desperate need to improve treatment options for late-stage prostate cancer patients,” said chief investigator Dr Johann de Bono, from the Institute of Cancer Research and Royal Marsden Hospital, based in London and Surrey.

“In this trial, abiraterone shrank or stabilised men’s cancers for an average of almost six months, which is a very impressive result.”

About three quarters of men experienced a drop in PSA levels, including a fall of at least 50% for around half of the patients in the trial.

The number of circulating tumour cells also fell in three quarters of cases, another measurement linked to increased survival rates. Many patients noticed a reduction in symptoms.

Five patients are still taking the drug and benefiting from treatment three years after the study started, said the researchers writing in the Journal of Clinical Oncology.

“Side effects from abiraterone were generally mild and easily treated,” said lead researcher Dr Alison Reid, from the ICR and Royal Marsden. “This is the first time the drug has been tested in prostate cancer patients with such advanced disease, who have already tried all the other effective treatments available to them.”

In the US, the men were treated at the Memorial Sloan-Kettering Cancer Centre and the University of California (San Francisco) Comprehensive Cancer Centre.

Because of the promising results, a decision has been taken to test the effectiveness of abiraterone in a large scale Phase III trial spanning 12 countries.

Professor Malcolm Mason, from the charity Cancer Research UK and Cardiff University School of Medicine, said: “These early results are extremely exciting but there’s a lot more work needed to establish what abiraterone’s place will be in treating men with prostate cancer.

“We eagerly await the results of ongoing studies of abiraterone in clinical trials as they will give us the most definite indication of what impact this drug might have in men with advanced prostate cancer.”

Abiraterone is a new kind of hormone therapy drug that works in a different way to others.

The drug neutralises an enzyme, cytochrome P17, that the body uses to make testosterone, the male hormone that fuels prostate cancer.

When prostate cancer becomes resistant to hormone therapy, it manufactures its own testosterone. But abiraterone blocks the production of testosterone in all tissues, including the tumour.

Each year, around 35,000 men in the UK are diagnosed with prostate cancer and 10,000 die from the disease.