You've got to hand it to Kelly Martin, the CEO of Elan (NYSE:ELN) -- he's certainly not one to give up in a fight.

Speaking to reporters after the company's annual meeting, Martin repeated his position that Tysabri, the company's multiple sclerosis drug co-marketed with Biogen Idec (NASDAQ:BIIB), will return to the market. As investors may remember, Tysabri was pulled by the two companies in February after three patients developed PML (progressive multifocal leukoencephalopathy) -- a rare and very dangerous disease of the brain.

What's most interesting to me about this is that it's not news, and yet the stock is up more than 10% today. Martin had already said in the past that he thought Tysabri would someday be relaunched, and Biogen Idec executives have echoed that sentiment -- the only difference today is that it seems that more people are paying attention to the statement (and Elan's stock has been strong of late anyway).

As Martin sees it, the question now is largely one of risk assessment between the two companies and the FDA. Biogen Idec and Elan are supposed to complete an internal review by the end of summer, and once that's finished they can engage the FDA on more substantive talks about how to bring the drug back onto the market.

There's no doubt that Martin has extended himself on this one. Should the FDA refuse to allow Tysabri back on the market, there will surely be a flurry of lawsuits directed at the company (sad that it's that predictable, isn't it?).

What's more, despite his optimism, this is no slam dunk. The FDA is in a very tight squeeze these days -- pressured by sick patients who want easier access to potentially lifesaving drugs and patient advocacy groups that seemingly want the FDA to hold up approvals until there's no doubt whatsoever about a drug's efficacy and safety.

I'd say that a best-case scenario at this point is that the FDA would permit a relaunch of the drug, but only with the infamous black-box warning label and perhaps an admonition to doctors not to use Tysabri unless their patients fail with other medicines. Of course, if the companies and the agency can come together and figure out why the drug triggers PML in some cases, then perhaps a broader relaunch would be possible (assuming, of course, that it's only a small group of patients that would be at risk).

In the past, I have gone on record stating that investors would do well to analyze and assess Elan as though Tysabri would never come back. To be completely honest, this is one case where I'd really, really like to be wrong -- MS is a terrible disease, and I have no doubt that Tysabri can help most of those who patients who take it. But it's still too hard to make any definitive predictions at this point.

The FDA seems to be in a cooperative mood these days (at least it was with COX-2 inhibitors), but without a sneak peak at the data, I just can't know how the agency is going to view Tysabri. So, here's my advice for now -- if you like Elan well enough to own it even if Tysabri never returns, stick with it. But if you're pinning your hopes on a full return on this drug, you might be signing on for more risk than you really want.

For more on Elan and the Tysabri matter:

Fool contributor Stephen Simpson has no financial interest in any stocks mentioned (that means he's neither long nor short the shares).