THOUSAND OAKS, Calif. (

TheStreet

) --

Amgen

(AMGN) - Get Report

said a late-stage clinical trial showed its experimental bone drug denosumab was equivalent to a competing drug from

Novartis

(NVS) - Get Report

in preventing fractures and other bone-related problems in patients with various types of cancer.

The phase III study -- the second of three such studies involving denosumab -- successfully achieved its primary endpoint, the company said Monday night. Positive results from the first phase III study of denosumab in breast cancer patients was announced last month.

Denosumab is the most important new drug to come out of Amgen's research labs in years and is key to the company's future growth as sales of its flagship anemia drugs, Epogen and Aranesp, have flagged in recent years.

The

Food and Drug Administration

is currently reviewing denosumab as a treatment for osteoporosis, with an approval decision expected later this year.

Amgen is also developing the drug as a treatment aimed at cancer patients, who often suffer fractures when tumors grow, or metastasize, into bones.

Amgen shares closed Monday at $62.88 ahead of the denosumab trial announcement, but fell 98 cents to $61.89 in after-hours trading. In Monday's study, denosumab was found to be equivalent to Zometa, whereas in the previous breast cancer study, denosumab was superior.

Advanced-cancer patients treated with denosumab reported a similar time before their first skeletal-related event to patients treated with Zometa, Amgen said. The result met the pre-defined primary endpoint of the study with statistical significance, Amgen said.

The phase III study enrolled 1,776 patients with solid tumors (excluding breast and prostate cancer) plus multiple myeloma,

A skeletal-related event was defined as a bone fracture, radiation to bone, surgery to bone or spinal cord compression.

The delay in first skeletal-related event was numerically superior for denosumab compared to Zometa but not enough to be statistically significant, Amgen said.

On the safety side, Amgen said the incidence of osteonecrosis, or death of bone, in the jaw was comparable for denosumab and Zometa patients.

The rate of infections, overall survival and time to cancer progression also were similar between patients treated with denosumab and those treated with Zometa.

-- Written by Adam Feuerstein in Boston

Adam Feuerstein writes regularly for TheStreet.com. In keeping with TSC's editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet.com. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback;

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