By Amy Norton
Experts said the results, published in the July 18 issue of the New England Journal of Medicine, offer some good news for men whose cancer has migrated to the bones -- a common and painful feature of advanced prostate cancer.
The drug, which is marketed as Xofigo, is intended for men with cancer that has spread to the bones despite standard treatment to cut the body's levels of testosterone -- the "male" hormone that fuels prostate cancer growth.
Known generically as radium-223, the drug emits radioactive particles that zero in on cancerous tissue in the bones. In the new study, researchers found that men given Xofigo had a lower death rate and better quality of life than those on standard treatment only.
Xofigo is already on the market in the United States, after getting an expedited approval from the U.S. Food and Drug Administration in May. That was based on findings from the current trial, which was designed and funded by drug makers Bayer and Algeta.
The study was supposed to last three years, but it was stopped early when interim results showed that men on the drug had a clear survival advantage.
Those patients typically survived for 15 months, versus 11 months among men who received an inactive placebo in addition to standard treatment.
That "might not sound like very much," said lead researcher Dr. Christopher Parker, of Royal Marsden Hospital in the United Kingdom. "On the other hand, this represents a 30 percent improvement in survival in a group of patients who had a very poor prognosis."
More important, the extra time tended to be better-quality time, said a cancer specialist who was not involved in the research.
If a cancer therapy gives people more months of life, but those months are filled with debilitating treatment side effects, then the longer survival may not be worth it, said Dr. Neha Vapiwala, a radiation oncologist at the University of Pennsylvania in Philadelphia.
"In this study, their quality of life was improved, in addition to their longer survival," she noted.
The study included 921 men with prostate cancer that had spread to the bones but not other organs. All had received standard hormonal therapy and, in some cases, the chemotherapy drug docetaxel. (Some men were not healthy enough to receive the chemo, and others did not want it.)
About 600 men were randomly assigned to have injections of Xofigo, once a month for six months; the rest were given placebo injections and standard care, including more hormonal therapy or external radiation to try to treat the bone pain.
At the time the trial was stopped, 35 percent of the Xofigo group had died, versus 46 percent of the placebo group. One-quarter of men on the drug reported a "meaningful" improvement in their quality of life, compared with 16 percent of the placebo group.
There were, though, more serious problems related to the body's ability to produce blood cells, which is handled by the bone marrow. Twelve percent of men on Xofigo developed thrombocytopenia, a drop in blood cells called platelets that can cause serious bleeding. That compared with 6 percent of the placebo group.
Another 5 percent of men on the drug developed neutropenia, a drop in the body's infection-fighting white blood cells.
For most men with prostate cancer, the tumor is slow-growing and never progresses to the point where it threatens their lives. According to the American Cancer Society, nearly all men with cancer confined to the prostate gland or nearby lymph nodes are still alive five years after their diagnosis -- and many can opt to delay having any treatment, and have the cancer monitored instead.
But the outlook is much more dim for men whose prostate cancer spreads to the bones or other distant sites. Only 28 percent are alive five years after their diagnosis.
"There are men who have serious disease, and in the years they do live they are often in pain, and in and out of the hospital," Vapiwala said.
Xofigo gives an option for at least some of them, she said.
Because the drug emits radioactive particles, it has to be given by a radiation oncologist or nuclear medicine specialist. So, smaller community hospitals may not be able to offer it, Vapiwala noted.
There's also cost. The course of six injections rings up at nearly $70,000.
The ultimate role of the drug in treating advanced prostate cancer is still in question, according to Vapiwala. A few other treatments -- hormonal therapy and two chemo drugs -- have been approved for these same patients in the past couple of years. And it's not known if Xofigo could, for example, be combined with any of those treatments.
"The right combination of treatments, and the right sequence, is still being studied," Vapiwala said.
And Parker added that no one knows yet if the drug could help people with other types of cancer that has spread to the bone. "In theory," he said, that should be the case. "But we do not yet have any data on this."
He noted that an ongoing trial is studying radium-223 for breast cancer that has spread to the bones.