NEW YORK - The single biggest issue that is significant enough to drive a double in Elan over the next two to three years is this: Will the FDA approve Tysabri for use in mono-therapy after Elan pulled it from the market?

We surveyed more than 1,500 members of Marketocracy who put Elan (nyse: ELN - news - people ) in their virtual portfolios to try to flesh out the answer. Three interesting perspectives emerged from the responses.

The FDA: For the U.S. Food and Drug Administration, the question of whether to allow Tysabri back on the market is one of benefits and risks. The main benefit is that two-year clinical studies have shown Tysabri, when used alone, is twice as effective as any other approved drug in preventing relapses. People who have used Tysabri have actually got out of their wheelchairs.

The main risk is that three patients have come down with a potentially fatal complication called progressive multifocal leukoencephalopathy, or PML--two have died. That's a complication rate of 0.1% out of 3,500 patients. All three cases involve patients taking Tysabri in combination with Avonex from Biogen (nasdaq: BGEN - news - people ). Since the three PML cases were discovered, 91% of the patients in Multiple Sclerosis clinical trials that took Tysabri have been screened for PML, and no additional patients have showed signs of contracting it. There has not been a single case of PML when Tysabri was used alone, but Elan voluntarily took it off the market.

The bottom line is the drug sets the gold standard for efficacy in a disease that is very nasty. Patients want this drug available because it is effective. I expect the FDA will decide that its benefits offset its risks--especially for patients for whom all existing drugs have failed.

Patients, Doctors and Caregivers: MS patients and the people who care for them understand that treating powerful diseases requires commensurately powerful drugs, and they understand that, because of potency, the drugs have potentially fatal consequences for some at-risk patients.

For almost 25% of MS patients, existing drugs have failed to be effective, so many have stopped taking any MS drug at all. Tysabri could be their best option. Most of the remaining MS patients report that the drugs they take do not work well. At best, they slow the progression of the disease, but there is a high relapse rate and many side effects.

So, given the almost 100% certainty of the progressive debilitating effects of the disease, most patients would opt for the rare possibility of PML if they could halt the progress of MS and improve the quality of their lives. A particularly poignant response I received was: "I participated in the AFFIRM trials and had Tysabri for nearly three years. I forgot what it was like to be an "MSer." Since Feb. 28, nearly all of my most annoying symptoms (itching, fatigue, brain fog) have returned, and I have had my first relapse in about four years."

Biogen: Biogen, the U.S. distributor for Tysabri, also owns a best-selling MS drug called Avonex. Typically, a drug has to be proved effective as mono-therapy before it is approved for combination therapy. Biogen pushed Tysabri's use in combination with Avonex, hoping to convince doctors to prescribe two drugs instead of one. Taking on Biogen as a partner created a conflict of interest.

With FDA approval of Tysabri in combination with Avonex looking remote, Biogen's next-best alternative is to return Tysabri to the market as quickly as possible. As a result, Biogen's interests are now much more aligned with Elan's.

Approval by the FDA of Tysabri for use in mono-therapy by the 20% to 25% of MS patients that have already given up on all other drugs would drive a double in Elan's stock price. Based on the feedback we've received from the people who are in the best position to judge, we believe that will happen. And if any of the remaining MS patients decide to give up on the less-effective drugs they are currently using to try Tysabri then Elan will do even better.

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