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Feb. 18, 2007 (San Francisco) -- A novel drug that blocks the production of male hormones anywhere in the body shows promise for curbing the growth of hard-to-treat prostate tumors.
The experimental agent, called abiraterone, reduced PSA levels by 50% or more in nearly half of 38 patients whose prostate cancer continued to spread despite standard therapy. In nine men, tumors shrank or stopped growing altogether.
PSA levels are a measure of a protein called prostate-specific antigen, which is produced by cells in the prostate. High PSA levels can signal cancer. Men with faster drops in PSA post-treatment tend to have more favorable outcomes after treatment.?
Daniel Danila, MD, a medical oncologist at Memorial Sloan-Kettering Cancer Center in New York, presented the results here at the 2008 Genitourinary Cancers Symposium. The meeting is cosponsored by the American Society of Clinical Oncology (ASCO) and two other cancer care organizations.
Prostate cancer grows when exposed to the male hormone testosterone and its related hormones, called androgens. When cancer spreads outside the prostate, treatment is given to halt the production of testosterone and androgens.
Current treatments -- surgical removal of the testes or medication -- prevent the production of male hormones in the testes. But these approaches do not prevent other parts of the body from making male hormones. Abiraterone targets proteins that are necessary to the production of male hormones throughout the body.
The new study involved men who had been surgically or medically treated to prevent testosterone production in the testes.
All the men had failed to respond to the chemotherapy drug Taxotere, the current treatment of choice for men whose cancer continues to grow and spread despite treatment with anti-hormone therapy.
They were given a pill of abiraterone daily. Three months later, 17 of the 38 men, or 45%, continued to experience a PSA drop of 50% or more.
The National Cancer Institute views a response to treatment as being seen when there is at least a 50% decline in PSA blood level.
"Some patients fail quickly and some go a long time without failing," Danila says.
"These were chemotherapy failures, so the 45% response rate seen in the study is very impressive," says ASCO spokesman Eric A. Klein, MD, head of urologic oncology at the Cleveland Clinic.
The high response rate suggests abiraterone may also be useful for the treatment of men with earlier-stage prostate cancer -- before it starts to spread and before doctors have to resort to chemo, he tells WebMD.
There drug was well tolerated, with no major side effects noted.
The study was funded by Cougar Biosciences, which makes abiraterone.
Prostate cancer is the second most common cancer among men. It is diagnosed in more than 218,000 men and claims more than 27,000 lives each year.