Amgen Inc. (AMGN) shares are showing resilience Friday, despite the biotech's miserable first-quarter sales performance, as investors bet that the situation can only get better with key catalysts emerging in coming months.

Shares of the Thousand Oaks, Calif., drug maker, down 19% in 2009 before today, rose 5% Friday to $49.18.

"We think at current levels, there is limited downside and numerous opportunities in coming quarters to see significant upside. We are buyers into the high $50s," said Christopher Raymond, analyst at Robert Baird & Co.

The key catalyst for Amgen is the experimental bone drug denosumab, seen going before the Food and Drug Administration in October for use in osteoporosis and having key data on its use in cancer patients coming later this year.

As a result, Amgen supporters argue, the downside to the company's stock price is limited because investors will buy into Amgen shares, especially when prices dip, to gain exposure for any potential denosumab upside later this year.

Plus, Amgen has been mentioned as a possible takeover target. While its current market cap of $50 billion would make any deal sizable, investors may buy whenever shares slide to their year lows, at $41.55, in case of that possibility.

Raymond said the bad quarter "clears the deck" for denosumab and that the stock is "too inexpensive to ignore" as he upgraded shares to outperform after spending two years urging investors to stay on the sidelines.

In comparison to its large biotech peers, Amgen shares look cheap. They currently trade at 10.7 times estimated 2009 earnings, compared to Celgene Corp. (CELG) at 20.4 and Gilead Sciences Inc. (GILD) at 18.

The discount likely reflects the issues highlighted by Amgen's disappointing first quarter, which showed sales weakness in its biggest drugs, leading the company to lower 2009 revenue guidance. Plus, skeptics note, risk remains that denosumab could disappoint.

Amgen has taken action to support its stock price by spending $2 billion in the first quarter to repurchase 38 million shares, reducing its shares outstanding by 4%. In all of 2008, the company repurchased 45 million shares.

Amgen shares have been volatile over the past two years, and calling a bottom can be dangerous.

The stock lost almost half of its value from early 2007 until hitting a low of $39.16 almost a year ago. The decline was driven by deteriorating sales of its anemia drugs amid safety and regulatory concerns.

During that long drop, many attempted to make the case of Amgen's value, only to be met with continued selling.

Deutsche Bank analyst Mark Schoenebaum recently called the stock his "personal Vietnam" during 2007, when he worked for a different firm, but Friday noted its attractiveness in the mid to low $40 range.

"Sentiment is horrible - so horrible that this could be the nadir," he said.

-By Thomas Gryta; Dow Jones Newswires; 201-938-2053; thomas.gryta@dowjones.com