SATURDAY, June 3, 2017 (HealthDay News) -- Men with advanced prostate cancer might be able to avoid chemotherapy by taking an additional anti-testosterone pill along with standard hormone therapy, a pair of new clinical trials show.
The drug, abiraterone (Zytiga), lowered patients' risk of death by nearly 40 percent when added to standard androgen deprivation therapy, both studies found.
Abiraterone also appeared to more than double the average time it took for a man's prostate cancer to progress, one of the studies reports.
Doctors currently combine the chemotherapy drug docetaxel with hormone therapy to treat patients with advanced prostate cancer, where the cancer has spread to the bone or other parts of their body, the researchers said.
Abiraterone now offers a reasonable alternative to chemotherapy for these men, said Dr. Sumanta Kumar Pal, an expert with the American Society of Clinical Oncology and associate professor of medical oncology and therapeutics research for City of Hope in Duarte, Calif.
"At first glance it appears as though the benefit and survival seen with abiraterone mirrors or exceeds the benefit we've seen with chemotherapy," with less toxic side effects, Pal said.
The results of these trials are "pretty likely to change clinical practice overnight," said ASCO Chief Medical Officer Dr. Richard Schilsky. The studies are being presented this weekend at ASCO's annual meeting, in Chicago.
More than 161,000 new cases of prostate cancer are expected to occur in U.S. men in 2017, nearly 10 percent of all new cancer cases, according to the National Cancer Institute.
About 3 percent of U.S. men newly diagnosed with prostate cancer have metastatic cancer, or cancer that has spread beyond the original tumor, said Dr. Karim Fizazi, head of cancer medicine at Gustave Roussy, University Paris-Sud in Villejiuf, France.
Testosterone fuels prostate cancer growth, so doctors use androgen deprivation therapy (ADT) to prevent the testicles from producing the male hormone. However, ADT drugs do not prevent the adrenal glands and prostate cancer cells from continuing to produce small amounts of testosterone, the researchers said.
Abiraterone, a pill taken once daily, blocks an enzyme that converts other hormones to testosterone, essentially halting production of testosterone throughout the body. The U.S. Food and Drug Administration previously approved abiraterone for patients with metastatic prostate cancer that didn't respond to regular androgen deprivation therapy.
The first clinical trial, called LATITUDE, involved 1,200 men with newly diagnosed, high-risk prostate cancer. The men all had at least two of three risk factors -- an aggressive prostate tumor, three or more bone tumors, or three or more tumors in other organs.
The patients were randomly assigned to receive either abiraterone or a placebo alongside standard hormone therapy. The abiraterone patients also were given prednisone, a steroid routinely prescribed with the drug to help control side effects like low potassium or high blood pressure.
At 30 months' follow-up, men treated with abiraterone had a 38 percent lower risk of death than those who got a placebo, and had a 53 percent lower risk of their cancer getting worse, the researchers found.
The drug also extended the average time it took for cancer to progress, from 14.8 months to 33 months.
Adding the abiraterone/prednisone combination to regular androgen deprivation therapy "should now be considered the new standard of care for these men," said Fizazi, who served as lead researcher for the clinical trial.
The second clinical trial presented at ASCO provided immediate support for the first study's results, Schilsky said.
The trial, called STAMPEDE, involved nearly 2,000 men with advanced prostate cancer who were starting hormone therapy, said lead researcher Nicholas James, a professor of clinical oncology at Queen Elizabeth Hospital in Birmingham, England.
The three-year overall survival rate was 83 percent in men taking abiraterone versus 76 percent in men receiving standard androgen deprivation therapy, James said.
Projections suggest that average survival will be about 6.5 years in abiraterone patients compared with 3.5 years for all the advanced prostate cancer patients, James said.
"We think this is one of the biggest survival gains ever reported in a trial in adults with solid tumor," he said.
Both studies reported side effects in abiraterone similar to those already found in patients taking the FDA-approved drug, researchers said.
High blood pressure occurred in 20 percent of patients treated with abiraterone, compared to 10 percent of placebo patients, in the LATITUDE trial. Other severe side effects included low potassium (10.4 percent versus 1.3 percent) and liver enzyme abnormalities (5.5 percent versus 1.3 percent).
Because of these side effects, Fizazi said doctors should be cautious when using abiraterone in men with an increased risk of heart problems.
However, Pal believes abiraterone could be used even in men with increased heart risk, as long as they are closely monitored.
James suggested that abiraterone could even be effective in men whose prostate cancer hasn't spread, but Pal said more research is needed to determine that.
Abiraterone costs about $5,000 a month, according to The New York Times.
Both clinical trials received support from abiraterone's manufacturer, Janssen Biotech.
For more on hormone therapy for prostate cancer, visit the U.S. National Cancer Institute.