Usually, confirmatory phase 3 trials don't cause 40% gains in a stock. Especially after the first one resulted in a crazy 500%-plus gain.

Then again, most drugs don't treat lupus.

There was still a lot of skepticism -- mine included -- going into today's data release for Human Genome Sciences' (NASDAQ:HGSI) lupus treatment, Benlysta. The drug passed its first phase 3 trial, which would normally give investors a lot of confidence that Benlysta would work in this trial, too. But that incremental addition in confidence doesn't bring you very high when your confidence in the drug started out so low; lupus is one tricky disease to treat.

Turns out the skeptics had nothing to worry about. In the second trial, Benlysta showed a statistically significant improvement in symptoms compared with the placebo. The results weren't quite as good as the first trial -- including missing three secondary goals at the highest dose -- but having two trials that passed their primary test should satisfy the regulators. It looks like Benlysta will be the first drug approved specifically to treat lupus in 50 years, succeeding where drugs from Biogen Idec (NASDAQ:BIIB), Teva Pharmaceutical (NASDAQ:TEVA), BioMarin Pharmaceutical (NASDAQ:BMRN), and others have failed.

So is Human Genome worth buying now that the fear of failure has subsided? Unfortunately, the awesome biotech returns have passed. Much of the potential sales are already priced into the company, which now has a market cap of more than $3 billion.

Human Genome receives revenue for sporadic sales of its anthrax treatment and has a hepatitis C drug candidate, Zalbin, that's expected to hit regulators' desks this quarter. The lackluster trial results from Zalbin, which is partnered with Novartis (NYSE:NVS), should be good enough to gain Zalbin marketing approval, but will make it difficult for the drug to compete against current offerings from Roche and Schering-Plough -- soon to be Merck (NYSE:MRK).

That leaves most of the company's value tied up in Benlysta. Human Genome and marketing partner GlaxoSmithKline (NYSE:GSK) expect to file marketing applications in the first half of next year, which puts an approval about a year away.

Even if Benlysta is the blockbuster everyone expects it to be, that's an awfully long time to wait with so much of the revenue already priced in.

BioMarin Pharmaceutical is a Motley Fool Rule Breakers pick. The newsletter team is always on the hunt for hot drug stocks and other cutting-edge picks. See all of our latest discoveries with a free 30-day trial. 

Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. Novartis is a Global Gains selection. The Fool has a disclosure policy.