Editor's Note: A version of this story appeared in the Dec. 17 print edition's healthcare and biotech industry column.

Amgen shares hit a five-year low on Monday, despite the company having released solid data over the weekend on a potential blockbuster osteoporosis treatment.

The Thousand Oaks-based biotech giant said late Friday that denosumab hit both its primary and secondary goals of increasing bone mass in women undergoing a breast cancer treatment that causes bone loss due to reduced estrogen in the body.

In a two-year study, presented at the annual San Antonio Breast Cancer Symposium, denosumab showed positive results compared with placebo. Denosumab, which is a injectible monoclonal antibody that researchers had been studying since the mid-1990s, works by blocking certain processes in the body that lead to bone loss.

As a potential treatment both for post-menopausal osteoporosis and bone loss related to certain cancer treatments for both women and men, some industry analysts believe denosumab could become another billion-dollar blockbuster, comparable to Amgen's now beleagured anemia drug Aranesp.

"Because these women also are post-menopausal this study is one in which our two therapeutic programs intersect," said Dr. Roger Dansey, Amgen's director of oncology global development for the drug.

Nonetheless, Amgen shares were $1.47, or 3 percent, to $46.93 in afternoon trading. Earlier Monday, shares fell as low as $46.89, the lowest since December 2002.

Some analysts questioned the drug's market prospects, noting that the denosumab data was in-line with some drugs already on the market. Amgen is conducting head-to-head study with Merck & Co.'s Fosamax, an oral drug which is due to lose patent protection in 2008.

"With limited long-term safety or fracture-risk data available, we believe physicians may be hesitant to prescribe denosumab in early-stage patients," said Lazard Capital Markets analyst Joel Sendek in a Monday note to investors.

Amgen hasn't yet announced when it plans to submit an application to the U.S. Food and Drug Administration, though Sendek anticipates a submission by the end of next year. The company has several studies ongoing, including one on denosumab's ability to counter bone loss in men undergoing similar treatments for prostate cancer.

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