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updated 7/17/2013 5:18:22 PM ET 2013-07-17T21:18:22

Men with advanced prostate cancer may live longer after receiving a new type of targeted radiation treatment, a new study suggests.

In the study, men given the treatment — a radioactive drug that specifically targets tumors in bone — lived 14.9 months on average after their diagnosis, while those who received the placebo lived 11.3 months, meaning the drug extended life by about 3.5 months.

All patients in the study had castration-resistant prostate cancer, which is cancer that comes back despite surgical or drug treatments to lower testosterone levels.

About 30,000 U.S. men die from prostate cancer each year, often from cancer that has spread to the bone. Many patients how have castration-resistant prostate cancer and bone tumors cannot receive chemotherapy because they are too frail, the researchers said. [See 5 Things You Should Know About Prostate Cancer ].

The new drug, called radium-223 dichloride (marketed as Xofigo), mimics calcium, and binds to parts the bone that are rapidly dividing — a characteristic of tumor sites. Because the radiation is targeted to the bone tumors, damage to other tissue, including bone marrow, is minimized, the researchers said.

"You're using a substance that naturally wants to go to where the cancer is," said Dr. Neha Vapiwala, a radiation oncologist and Associate Professor at the University of Pennsylvania, who was not involved in the study.

The treatment also had the additional benefit of improving quality of life, such as relief from pain, for some patients, Vapiwala said.

The Food and Drug Administration approved the drug, called Xofigo, in May, based on early results from the study. The study was funded by Bayer HealthCare, which makes Xofigo.

The drug has the potential to be used to treat other cancers that spread to bone, Vapiwala said.

Improved survival

The study included 921 men in 19 countries with castration-resistant prostate cancer that had spread to their bones, but not to other organs. All patients had symptoms such as bone pain or fractures. The average age was 71.

Patients were randomly assigned to receive either an injection of radium-223 every four weeks (a total of six injections), or a placebo. All patients received the best care for their disease, which often included other treatments, such as radiation treatment and hormones to block the production of testosterone.

At the end of the study, 528 patients had died, including 54 percent of those in the radium-223 group, and 64 percent of those in the placebo group.

Radium-223 did not increase the risk of serious side effects compared to the placebo. The most common side effects were nausea, diarrhea, vomiting and swelling of the leg, ankle or foot.

The study is published in the July 18 issue of the New England Journal of Medicine.

Concerns about cost

Dr. David Samadi, chairman of urology at Lenox Hill Hospital, said that drugs like Xofigo are last-resort treatments for prostate cancer, used when other treatments such as surgery and radiation have failed to thwart cancer progression. While other drugs exist for advanced prostate cancer, so far, they are similar in effectiveness, adding about two to three months of life, Samadi said.

One concern about these new treatments is their high cost — Xofigo costs $69,000 for six injections, Bayer said.

"They're adding two to three months, for a huge cost. The question is, for someone who is dying, what do those three months mean?" Samadi said. Doctors and patients need to weigh the risks and benefits of the drugs before deciding to use them, he added.

Another treatment, called Sipuleucel-T (Provenge), a prostate cancer vaccine, costs nearly $100,000 and extends life by about four months.

Bayer and the company partner Algeta "are committed to ensuring that patients who lack insurance or have other financial needs and who need Xofigo have access to the treatment," Rose Talarico, deputy director of communications at Bayer, said in an email to LiveScience. The companies have set up a program to assist in obtaining coverage for patients who need it, Talarico said.

It's not clear if the drug would help patients with castration-resistant prostate cancer that has spread to other organs in addition to bone. Up to 25 percent of patients with castration-resistant prostate cancer have tumors that spread to internal organs, the researchers said.

Follow Rachael Rettner@RachaelRettner. FollowLiveScience@livescience,Facebook&Google+. Original article on LiveScience.com .

© 2012 LiveScience.com. All rights reserved.

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