AstraZeneca's (NYSE:AZN) Iressa had such potential. The lung cancer therapy was given an accelerated approval by the Food and Drug Administration in 2003, based on promising initial trial results.

But the follow-up trial 18 months later showed that patients didn't really live longer on the drug, and Iressa got about the harshest label any drug could get -- the FDA recommended that the only patients who should use the drug were those who had already taken it. Whoa! It's a little hard to grow sales with a label like that.

Iressa is trying to make a comeback, though. A study just published in the Lancet medical journal showed that the drug kept patients alive about as long as patients on docetaxel, the active ingredient in Sanofi-Aventis' (NYSE:SNY) Taxotere. Will the data help Iressa launch the comeback of the century? That's probably about as likely as Menudo making it big again. (Sorry, Menudo fans.)

First off, doctors don't like mixed results. Just as investors would rather invest in companies with decent earnings quarter after quarter, rather than ones with fluctuating bottom lines, doctors are likely to avoid prescribing drugs that have mixed results.

More importantly, there are a lot of options for treating lung cancer patients. Tarceva, from OSI Pharmaceuticals (NASDAQ:OSIP) and Genentech (NYSE:DNA), is available now, as is Genentech's Avastin. More treatments are on the way. Bristol-Myers Squibb's (NYSE:BMY) and ImClone Systems' (NASDAQ:IMCL) -- soon to be Eli Lilly's (NYSE:LLY) -- Erbitux is likely to be approved by the FDA after reporting decent survival data in lung cancer patients.

This latest trial, which was paid for by AstraZeneca, seems like a waste of money to me. Instead of throwing good money after a bad drug, AstraZeneca should just cut its losses and move on. It's disappointing to see a drug with such potential go down in flames, but that's the way the drug business works sometimes.

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