Drug Fights Resistant Prostate Tumors
Abiraterone Takes Different Tack to Combat Cancer
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
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.
How Abiraterone Works
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.
Abiraterone Lowers PSA
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.