By Tess Stynes

Gilead Sciences Inc.'s (GILD) fourth-quarter earnings rose 15% as the biopharmaceutical company reported double-digit revenue growth, mostly driven by strong sales of its HIV drugs.

Shares were up 2.3% % at $40.49 in recent after-hours trading Monday as adjusted earnings and revenue beat expectations. Through the close, the stock is down 3.8% from an all-time high of $41.14 on Friday.

Gilead's stock surged last year amid investor expectations for its new four-in-one HIV treatment Stribild and the potential for its investigational hepatitis C drugs. But the company also faces major challenges as patents on more than a dozen of its drugs, including several of its biggest sellers, expire over the next decade.

Gilead earlier Monday said its experimental liver disease pill was successful in two late-stage trials that will support a regulatory filing to market the first noninjectable treatment for hepatitis C. Gilead is still seen as the front-runner to bring a new generation of hepatitis C drugs to market and the first to capitalize on what is thought to be a multibillion-dollar opportunity.

The company has been aggressively looking to broaden its drug pipeline beyond the HIV and AIDS drugs that generate the vast majority of its revenue. Gilead in December agreed to buy Toronto-based YM BioSciences Inc. (YMI) for $510 million as it aims to boost its cancer-drug portfolio. Gilead acquired hepatitis C drug maker Pharmasett Inc. for $11 billion in January 2012.

For the latest quarter, Gilead reported a profit of $762.5 million, or 47 cents a share, up from $665.1 million, or 43 cents a share, a year earlier. Excluding acquisition- and restructuring-related charges, stock-based compensation expenses and other items, adjusted earnings were up at 50 cents from 49 cents per share. Revenue increased 18% to $2.59 billion.

Analysts polled by Thomson Reuters most recently projected earnings of 48 cents per share on revenue of $2.43 billion.

Operating margin rose to 42.8% from 39.4% amid the sales growth.

Stribild, Gilead's newest HIV treatment, which was launched in late August, contributed $40 million of sales in the latest quarter.

Complera/Eviplera sales surged to $117.8 million from $19.7 million a year earlier, while sales of HIV drugs Atripla and Truvada improved 6% and 12%, respectively.

Write to Tess Stynes at tess.stynes@dowjones.com

Subscribe to WSJ: http://online.wsj.com?mod=djnwires