New pill helps shrink prostate tumors: study

LONDON (Reuters) - A once-a-day pill significantly shrank tumors in men with advanced prostate cancer who had not responded to other treatments, researchers said on Tuesday.

Cougar Biotechnology Inc's drug abiraterone delayed a worsening of the disease by a median of 400 days, according to the Phase I clinical trial results published in the Journal of Clinical Oncology.

"We are highly confident this drug is highly active and durable," Johan de Bono, the researcher at Britain's Institute of Cancer Research who led the study, said in an interview. "We believe this drug will make a difference."

Prostate cancer is the second-leading cancer killer of men after lung cancer. Each year, 680,000 men worldwide are diagnosed with the disease and about 220,000 will die from it.

All the volunteers in the study had an aggressive form of prostate cancer in which some researchers believe the tumor tissue is able to produce its own supply of the hormones that fuel the disease.

"This drug prevents the cancer from making its own hormones that allow the cancer cells to survive," de Bono said.

The drug targets an enzyme called CYP17, which plays a key role in this process, he said.

About 70 to 80 percent of the men in the study showed declines in PSA levels and their tumors shrank, even when the cancer had spread to other parts of the body, de Bono said.

Prostate-specific antigen, or PSA, is a protein produced only by prostate cells. PSA goes up as the prostate enlarges, but it also rises if there is a tumor in the gland.

"Abiraterone works not only in blocking the generation of these hormones in the testes, but also elsewhere in the body, including generation of the hormones in the cancer itself," de Bono said.

The researchers said some volunteers have been on the drug for up to two-and-a-half years and were able to control the disease with few side effects. They included fatigue and weight gain, they added.

The drug is now in Phase III trials and de Bono said they hope to have it on the market in 2011. It has gone from Phase I to Phase III in under three years.

(Reporting by Michael Kahn; Editing by Maggie Fox and Angus MacSwan)