Melanoma is one tough cancer to treat. Except for Bristol-Myers Squibb's (NYSE: BMY) ipilimumab, there haven't been too many positive results in fighting skin cancer.

But Eli Lilly (NYSE: LLY) doesn't look like it's even going to get far enough to see whether its drug, tasisulam, works against skin cancer; the company put a trial on clinical hold because of "safety concerns."

Eli Lilly didn't disclose exactly what the safety issue is -- no need to tip off the competition, I guess -- but it must have been pretty bad to stop the trial. The side effect of not treating melanoma -- death -- isn't an ideal outcome, either. Bristol-Myers' Taxol, to which tasisulam was being compared, has some pretty nasty side effects of its own, including a boxed warning about hypersensitivity in 2% to 4% of patients.

Tasisulam is also being tested in a range of other cancer types, but at this point, the safety signal isn't affecting those trials, because the dose in the melanoma trial is different.

Eli Lilly can't really afford too many misses from its late-stage compounds. Diabetes drug teplizumab and Alzheimer's drug semagacestat both failed this year. And Bydureon, which it's developing with Amylin Pharmaceuticals (Nasdaq: AMLN) and Alkermes (Nasdaq: ALKS), is stuck in regulatory hell. Add the loss of many top-selling drugs over the next few years, and Eli Lilly isn't looking too healthy.

The optimists will say we don't know enough to make an opinion. Maybe tasisulam isn't dead; maybe there's a lower dose that still works but doesn't cause the mystery side effect. Maybe Eli Lilly and its partners will figure out a quick way to get the Food and Drug Administration the data it needs. Maybe. Maybe. Maybe.

Until Eli Lilly is consistently having more hits than misses, I'm definitely staying away, even at these beaten-down prices.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Fool has a disclosure policy.