(This story has been posted on The Wall Street Journal Online's Health Blog at http://blogs.wsj.com/health.) By Jennifer Corbett Dooren The Food and Drug Administration questioned the clinical benefit of using Amgen's bone drug Xgeva to prevent or delay the spread of prostate cancer to the bones. Xgeva is currently approved to delay fractures and other bone injuries in patients whose cancers have already spread to the bones. The company is seeking approval for use of Xgeva to prevent the spread of prostate cancer in a group of men that has not responded to other therapies. Xgeva will be reviewed Wednesday by the FDA's oncologic drugs advisory committee, which is made up of non-FDA medical experts. The FDA today posted a review of Xgeva in preparation for the meeting. Amgen conducted a study of Xgeva in 1432 men with prostate cancer that had not responded to previous therapies, but had not spread to the bones. Many types of cancer spread to the bones and cause tumors to grow, destroying the bone around the tumor, causing fractures and other problems. Half of the men were treated with Xgeva while the other half received a placebo. The study examined the time until men developed bone metastases or died, whichever occurred first. The study showed Xgeva prolonged median bone metastatis-free survival by 4.2 months compared to men in the placebo group. While the FDA said the study met its primary objective, the agency said it was unclear whether the results were "clinically meaningful" given that there was no difference in overall survival between the two patient groups. The agency said the risk-benefit ratio of Xgeva must also take into account the overall toxicity of the drug. One of the side-effects includes a risk of developing osteonecrosis of the jaw, or ONJ, a rare jaw-decay problem. Michael Severino, Amgen's vice president of research and development, said today that the company believes Xgeva does provide a clinically meaningful benefit because it delays the spread of cancer to the bone, which causes significant pain and other problems such as incontinence. Xgeva is also sold under the brand name Prolia as an osteoporosis treatment but is administered at a lower dose and less often than used to treat cancer-related bone complications. Xgeva and Prolia's combined sales in 2011 topped $550 million. The drugs target a protein called RANK Ligand, which helps regulate cells called osteoclasts that break down bone. (This post originally ran on Dow Jones Newswires.) -For continuously updated news from The Wall Street Journal, see WSJ.com at http://wsj.com.