Biotech investors had circled Oct. 19 as the day that Amgen Inc.'s (AMGN) osteoporosis drug denosumab gets approved, but they may have to wait longer.

Denosumab, a potential game-changer for the Thousand Oaks, Calif., company, is expected to be the most notable launch in the biotech industry in years. However, many on Wall Street expect the decision to be delayed, possibly by three months, because the Food and Drug Administration has a history of missing deadlines and may want more time to analyze the safety record of a new drug like denosumab.

"It would not surprise me to see the timeline slip," Credit Suisse analyst Michael Aberman said.

He believes a delay is already reflected in the stock, with limited downside, but that an on-time approval decision could move the stock into the mid-$60s. Amgen shares recently traded up 1.7% to $60.28.

Amgen officials didn't answer questions related to the issue. The company reports third-quarter results on Oct. 21.

A 90-day delay, during which the FDA could OK the drug at any point, might push approval into next year. A protracted delay would be negative because it forces investors to change their launch expectations and subsequent 2010 sales projections.

Osteoporosis treatments aren't new to the FDA, and there is a competitive market led by a cheap oral generic of Merck & Co.'s (MRK) Fosamax. But denosumab works through a new mechanism, by blocking a protein that is involved with bone destruction, and the agency is likely to be cautious before clearing it.

Furthermore, it will be the first biologic therapy - a drug made from biological processes - to be sold to primary care physicians, aside from vaccines. That target population means investors are closely watching the label warnings and risk management strategy related to the drug.

To be sure, the drug is widely expected to get approval, as it has the support of six Phase III trials involving more than 11,000 patients, with a relatively clean safety profile.

Despite the delay and crowded market, denosumab is expected to see quick adoption among some patients, because it is injected just under the skin twice a year and used by patients that can't tolerate bisphosphenates, the drug class of current popular therapies.

Amgen doesn't need to corner the market; Aberman's peak U.S. sales estimate of $1.3 billion in osteoporosis assumes that denosumab will grab only 16% of the market.

Still, many see a bigger opportunity for denosumab in treating bone complications in cancer, where Amgen is expected to file for approval next year. UBS recently projected that total worldwide sales will reach $2.5 billion for 2013, with additional indications possibly adding more momentum to its sales.

Amgen already sells a number of blockbuster products, but its troubles in recent years have made it more dependant on the success of denosumab. It has struggled with safety and reimbursement issues related to its anemia drugs, increased competition for arthritis-treatment Enbrel, as well as exposure to looming health care overhaul and generic biologics.

"It is transformative in the sense that this drug will put them back on the road to growth," Aberman said.

Indeed, denosumab has reinvigorated Amgen's stock by driving it up 31% since hitting a 52-week low in April. But long-term investors may be hoping for more as the shares hit an all-time high of $86.92 in September 2005 and first crossed the $60 mark almost ten years ago.

Regardless, little is likely to occur until some clarity comes from the FDA.

"For the time being, we think the stock is going to be range-bound," Citigroup analyst Yaron Werber said.

-By Thomas Gryta, Dow Jones Newswires; 212-416-2169; thomas.gryta@dowjones.com