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Prostate Cancer Drug Zytiga May Extend Life

The newly approved prostate cancer pill Zytiga (abiraterone acetate) may extend life by up to four months among men with spreading cancer who have already been treated with chemotherapy, a study shows.

May 25, 2011 -- The newly approved prostate cancer pill Zytiga (abiraterone acetate) may extend life by up to four months in men with spreading cancer who have already been treated with chemotherapy, a study shows.

This survival gain "means quite a bit," says study researcher Howard I. Scher, MD, chief of the genitourinary oncology service at Memorial Sloan-Kettering Cancer Center in New York City. "These are a group of patients for whom there is no standard of care and it is particularly gratifying to see these results, to say the least."

The new study is published in the New England Journal of Medicine.

Prostate cancer is the most common cancer diagnosed in men besides skin cancer, according to the American Cancer Society. One out of every six men will be diagnosed with prostate cancer during his lifetime.

The new drug, which was approved by the FDA in April, inhibits a protein that helps form male hormones. The findings may help reshape the way doctors view and treat advanced prostate cancer.

The new study included 1,195 men with metastatic prostate cancer whose disease had progressed after chemotherapy. Those men who received steroid therapy along with the new pill survived for 14.8 months, on average, compared with 10.9 months seen among those who received a placebo along with steroids. This translated into a 34% reduction in risk of dying, the study shows.

This survival edge was considered so significant that men who received the placebo were permitted to switch to the new drug before the study was completed.

Men who took the new pill also saw greater responses in levels of prostate-specific antigen (PSA) than men who received placebo. Elevated levels of PSA may be a marker for prostate cancer.

The men who took Zytiga also showed improvements in disease-related symptoms and prostate cancer progression on imaging tests compared with men who received the placebo.

Zytiga side effects included fluid retention, high blood pressure, and a drop in blood potassium levels.

Drug May Have Wider Role in Treatment

This group of patients is likely the tip of the iceberg as far as the role that the new drug can play in prostate cancer treatment, Scher says.

"It absolutely will work in untreated patients as well and clearly there are studies ongoing now that are looking at this drug in combination with standard hormone therapies prior to [prostate-removal] surgery," he says.

One mainstay treatment for spreading prostate cancer is to deplete or block the action of male hormones known as androgens. This typically works initially, but the cancer eventually progresses even though levels of male hormones are low. Until recently, researchers assumed that tumors became resistant to hormonal therapies.

The opposite may be true. "These tumors may actually be hyper-sensitive to hormone therapies," Scher says. "Androgen levels are higher in the tumors than in the normal prostate."

American Cancer Society Chief Medical Officer Otis Brawley, MD, explains it this way: "Hormonally unresponsive prostate cancer is really just incredibly sensitive to hormones. We have even taken away hormones from these guys through medical or surgical castration or androgen blockers and the tumor responds, but then starts growing again."

"It may be the tumor changes, so it is very sensitive to the small amount of androgen in the man's body," Brawley says. The drug interferes with the tumor's handling of that small level of androgen that was left behind.

New Treatment Option

"There has been a lot of buzz and excitement about this drug for a while," Brawley says.

Having another option to treat these men is "incredibly important," he says. "There are clear, definite gains in survival. Yes they are small, but they are clear, definite gains. And because of the rigorous design of this trial, there is no doubt that this drug works."

Study researcher Christopher J. Logothetis, MD, chair of the department of genitourinary medical oncology at the University of Texas M.D. Anderson Cancer Center in Houston, says this study is important on several levels.

"There is a new effective drug for patients with [spreading] prostate cancer, and it's nontoxic, relieves symptoms, and prolongs survival. That is exciting," he says.

"This indicates that even among patients who have run out of all alternatives, abiraterone prolongs survival by a third," he says.

Going forward, researchers may be able to identify a subset of men who will derive an even greater survival edge with the new pill, he says.

It may also become the "foundational drug" that is added to other medications to prolong survival even further, he says, adding that such combinations are already being developed and studied.

The drug is manufactured by Centocor Ortho Biotech Inc. The company provided support for the new study, and some of the study researchers have received consulting fees from them.

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