If you assume that Tysabri peak sales are cut in half, then based on Davis' math, the drug is worth about $7 a share to Elan. If Tysabri's sales are cut by a third, it's $9 a share in value.

Either way, that works out to an Elan stock price, excluding bapineuzumab, of $10-$12 a share -- a very, very rough guesstimate, for sure. Thursday night, tthe stock was trading at $11.55.

If the market is overreacting to the Tysabri-PML news because new cases of the brain infection were expected, Tysabri sales may remain relatively unaffected. But even if that's the case, I still think Elan is only worth $18 to $22 a share.

More on Elan from Stanley W., who wrote:
"I don't understand how Kelly Martin could be so bullish on bapineuzumab based on this data. Did he mislead us all?"

Kelly Martin, Elan's CEO, has a BIG credibility problem with Wall Street. Without naming names, let's just say that I saw a couple of Elan's largest institutional shareholders at the ICAD conference Tuesday night, and they looked like they wanted to take Martin into an alley and, well, you get the idea.

In an interview with CNBC Wednesday morning, Martin tried to blame Elan's selloff on too-high expectations and investors who want simple answers to complex questions.

That's laughable. It was Martin, himself, who set those high expectations for bapineuzumab, and the data aren't difficult at all to understand.

And it's Martin who fostered an arrogant, insular culture at Elan where friends were rewarded and anyone who dared question the company was frozen out. Now he wants to blame investors for the bapineuzumab fiasco? How lame.

And now, Martin has an even bigger problem on his hands because few investors will give him the benefit of the doubt when he tries to soothe investor nerves about Tysabri.

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