May 16 (Bloomberg) -- Amgen Inc.'s experimental drug denosumab was more effective than Novartis AG's Zometa in preventing fractures in cancer patients, according to early test results.

Denosumab reduced the risk of fractures in 64 percent of patients, compared with 37 percent of those taking Zometa, according to preliminary data released yesterday by the American Society of Clinical Oncology. The trial of 111 people included mostly patients with breast and prostate tumors, two types that often spread to the bones as cancer worsens.

Amgen, the world's biggest biotechnology company by sales, also is testing Denosumab in osteoporosis, bone loss caused by aging, where it might grab share from Merck & Co.'s Fosamax and generate as much as $3 billion a year, Sanford Bernstein & Co. analyst Geoffrey Porges said. Getting approved to halt cancer's spread to bones could yield annual revenue of $1 billion, analysts said.

``Denosumab has an easier route to market in cancer, but the big payoff would be osteoporosis,'' said Jim Reddoch, an analyst with Friedman, Billings, Ramsey & Co. in Arlington, Virginia, in a telephone interview.

Amgen fell 2 cents to $42.03 at 4 p.m. New York time in Nasdaq Stock Market composite trading. The stock has fallen 23 percent in the 12 months before today.

More complete results from the trial will be presented at ASCO's meeting May 30 to June 3 in Chicago.

Genetically Engineered

Denosumab, a genetically engineered antibody, is designed to block the action of a protein called RANK Ligand, which activates signals that lead to the breakdown of bones. Zometa, from a class of bone-strengthening drugs known as bisphosphonates, is approved for cancer patients whose disease has spread to bones.

Amgen plunged 32 percent last year in Nasdaq trading after its top-selling anemia medicines, Aranesp and Epogen, were linked to risks of tumor growth and death. The company, based in Thousand Oaks, California, is testing six new cancer medicines in more than 30 trials planned or under way.

In preliminary results of another denosumab trial released yesterday by ASCO, denosumab helped shrink or slow growth of bone tumors in 13 of 15 patients. Amgen is moving forward with larger human trials.

To contact the reporter on this story: Lisa Rapaport in New York at Lrapaport1@bloomberg.net

Last Updated: May 16, 2008 16:19 EDT