Much of Amgen's (AMGN) future rests on its experimental bone drug denosumab, to be sold commercially as Prolia. The drug has had its ups and downs, but Amgen, the largest global biotech company, said on Monday that a pivotal third Phase 3 clinical trial pitting denosumab against Novartis's (NVS) Zometa showed that denosumab worked better.Amgen said the trial of 1,901 patients met its primary and secondary goals: to demonstrate its drug's superiority in delaying the time to the first on-study skeletal-related event, such as a fracture or spinal cord compression, and reducing the rate of multiple events in men with advanced prostate cancer.

"These Phase 3 results demonstrate the ability of denosumab to delay bony complications in patients suffering from metastatic prostate cancer," said Roger Perlmutter, Amgen's head of Research and Development.

Questions From the FDA

The company has long billed denosumab as a future blockbuster. When Amgen released similar results in July in a study of breast-cancer patients, shares jumped 15%. But denosumab has since met resistance: It's under review by the Food and Drug Administration for several uses, including postmenopausal osteoporosis and as a treatment for bone loss in breast and prostate-cancer patients undergoing therapy. In August, an FDA panel expressed concern over the drug's safety and voted against using it to prevent postmenopausal osteoporosis, or in breast cancer patients with osteoporosis. In October, the FDA requested a risk-mitigation plan.

And as Amgen's anemia drugs continue to encounter difficulties, denosumab was supposed to replenish lost sales and provide growth. The U.S. osteoporosis market is estimated at $8.4 billion, and U.S. patients with bone metastases incurred $12.6 billion in costs in 2008.

Credit Suisse has estimated that sales of denosumab could total $3 billion by 2013. A Cowen analyst estimates denosumab sales as high as $6 billion by 2015. Barclays, too, was encouraged by the results, while Oppenheimer recommended a buy, predicting that the drug will be approved by the FDA in 2011.

Pivotal Study

Amgen didn't provide details, saying it would report full results in June, but did say that the overall adverse events, including infections, were generally similar between the two treatment groups. Also, both patient survival and the time to cancer progression were similar for both drugs in the prostate cancer trial.

The company also reported that osteonecrosis of the jaw -- deterioration of the jaw bone -- was seen in 22 patients receiving denosumab, compared with 12 patients receiving Zometa. In addition, the incidence of hypocalcemia, or low blood calcium levels, was more frequent in the denosumab arm.

Amgen said it plans to submit the results, along with results from the two earlier cancer patient trials, to U.S. regulators this year. Data is expected this year from a study examining whether denosumab can prevent cancer from spreading to the bone in the first place, which could add to its market potential.

Denosumab is a genetically engineered drug, first in its class that specifically targets RANK Ligand, the essential regulator of osteoclasts (the cells that break down bone). Amgen is studying denosumab in numerous tumor types.

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