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What a crazy week! The Biotech Mailbag is brimming with email, so let's get to it.

The big story, of course, was the meltdown of Elan ( ELN) Wednesday after its Alzheimer's drug fell flat on its face at the International Conference on Alzheimer's Disease meeting in Chicago.

I've been a vocal skeptic of Elan and its Alzheimer's drug bapineuzumab this year, a bearish position that hasn't always been a comfortable one to take. Needless to say, I felt vindicated and it was nice to receive a bunch of emails acknowledging my work.

"You were right on target. Props," wrote Charles B.

From Vince M.: "Congrats on the Elan call. You were right."

I even heard from an Elaniac, a guy known only as snugpharma. "Today, you win. In the future, well, in this chastened mood, I am not really up for the fight at this time."

Enough back-slapping. Most of the email I received on Elan this week was from readers who want to know what happens next, like Gerry W., who wrote:
"Hey Adam, the Elan column was a great read. I'm wondering, however, what happens to the company and the stock now that the ICAD conference is over?"

Gerry's email arrived before Thursday's night bombshell, when Biogen Idec ( BIIB) and Elan disclosed in a regulatory filing two new cases of a serious and often deadly brain infection in multiple sclerosis patients being treated with Tysabri. In fact, I wrote this entire column before the Tysabri news hit the wires.

In version one of this week's Mailbag, written with the sun high on a hot and humid Thursday afternoon, I intended to tell Gerry that Elan was in a real bind because of bapineuzumab. It's late Thursday night, dark but still hot and humid, as I rework Mailbag version No. 2 to reflect the Tysabri situation.

Needless to say, Elan's outlook doesn't look any brighter.

Is there any compelling reason to own Elan now? Bapineuzumab looks like a crapshoot at best, and news flow around the program goes dark as the phase III studies enroll patients and we wait two years for data. Many bulls were hoping for an early or accelerated approval filing. Please, the bapineuzumab data are so weak, that rosy scenario is now pure fantasy.

Add in Tysabri uncertainty. Re-occurrence of the serious brain infection known as progressive multifocal leukoencephalopathy (PML) was expected -- warnings are in the Tysabri label -- and the two patients diagnosed with PML are alive. That's where the good news ends because it seems likely that doctors will be much more cautious about prescribing Tysabri to their multiple sclerosis patients going forward.

Sure, the diehard Elan bulls may hang on somewhat, but many of them were selling Wednesday when the bapineuzumab data came up lame. The hit from Tysabri, just a day later, is like the Wall Street version of a waterboarding. Even the very strongest hands are likely to succumb.

Consider this: The value of Fidelity Investment's massive 15% stake in Elan fell more than $900 million after the bapineuzumab data were presented. Based on Elan's after-hours swoon Thursday, the value of Fidelity's Elan investment fell $1.5 billion.

Even for Fidelity, that's a lot of money. If the mutual fund giant starts selling Elan, if it hasn't already, the stock is not going to recover anytime soon.

Let's talk valuation. Natixis Bleichroeder analyst Corey Davis, a table-pounding Elan bull, pegged Tysabri's value at $13 a share. That was before the new cases of PML popped up. He gave Elan another $3 a share in value for the base business, which includes drug delivery, and $24 a share for bapineuzumab.

Davis is not giving up on bapineuzumab, in fact, he appears to be doubling down, but just about everyone else is. So, scratch the $24 a share from his model and you're left with Elan trading at $16 a share, before this latest Tysabri scare.

The European pharma analyst at UBS puts Elan's fair value, ex-bapineuzumab, at $18 a share. That's the same guess at valuation offered to me by several Elan short-sellers Wednesday at the ICAD conference, by the way. Again, this is all before Thursday night's Tysabri shocker.

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.

I received a few barbed emails from folks angry that I ended this Elan column Wednesday by stating that I "felt a whole lot better" after bapineuzumab's stumble.

"MM" emailed to say he thought the comment was "disgusting."

"I have no idea how you can feel a 'whole lot better' when an Alzheimer drug fails," he added. "Millions of people suffer from this devastating disease and you're happy because a drug failed and you were right and some shorts made some money? Absolutely disgusting. Writers for Wall Street rags have no soul."

My joy this week comes from being right about the stocks I cover in this column and others. That's what I do -- I write about stocks. When those stocks behave the way I predicted they would -- up or down -- I'm happy. When they don't, no one is more angry at myself than me.

If you invest in biotech stocks, your main concern should be the performance of those stocks. You should be making investment decisions based on whatever flavor of stock-picking floats your boat -- fundamentals, charts, momentum, value, growth, etc.

What you shouldn't be doing is getting emotionally involved in your stocks. Sure, that's tougher in biotech since many of these companies are seeking cures or treatments for horrible diseases. But once you become a cheerleader for a cure, you're no longer an objective investor. In other words, you're in trouble.

Alzheimer's is a horrific disease that affects millions of people and their families. I hope that one day someone develops a drug that can treat Alzheimer's effectively. But I don't write about Alzheimer's disease or cancer or AIDS. I write about the stocks of companies that seek to develop drugs for those diseases. Those are two very different things.

Moving on. It was also a great week because Vanda Pharmaceuticals ( VNDA) received a non-approvable letter for its schizophrenia drug Fanapta -- another prediction of mine in the win column.

The Vanda news prompted Steve P. to write:
"The world, as we know, is coming to an end if a straightforward rational assessment of clinical trial data actually results in a logical, predictable response by the FDA. Congrats -- I am just amazed that there seems to be so much surprise by those who ought to know better."

I couldn't agree more, and I love Steve's snark. There are people out there doing the real work who get stuff like predicting the Food and Drug Administration's takedown of Vanda correct. I'm fortunate to know one of those guys because he makes me look smarter than I am.

Go back to my January column on Vanda. My source, a hedge fund analyst, said that FDA would issue a non-approvable letter based on his analysis of the company's clinical trial data. He nailed it cold.

Lastly, an email from David K., who asks: "Who is the best CEO in the pharmaceutical industry?"

I don't follow Big Pharma all that closely, so I hope David doesn't mind if I tweak his question towards biotech CEOs.

Genentech's ( DNA) Art Levinson has to be in the top tier, as does Gilead Sciences' ( GILD) John Martin. Myriad Genetics ( MYGN) isn't a pure biotech, but the way CEO Peter Meldrum managed to get $100 million from Lundbeck for a failed Alzheimer's drug that actually pushed his stock higher puts him in the genius category. BioMarin's ( BMRN) J.J. Bienaime has done a marvelous job turning around that company into one of the best-performing mid-cap stocks in the sector.

This isn't an exhaustive list, so let me turn the question around to all of you. Send me your pick for the best CEO in biotech. At the end of the year, I'll pick a winner and we'll celebrate his (or her) greatness right here.

And remember, I'm still seeking nominations for worst biotech CEO of the year. Elan's Martin appears to be making a strong run now, but who else do you think deserves the ignominy?

In the coming weeks, be on the lookout for a brand new product from Adam Feuerstein and TheStreet.com! Should you wish to hear more about this special invitation and how you can take advantage of some exciting pre-launch offers please email.

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Adam Feuerstein writes regularly for TheStreet.com. In keeping with TSC's editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet.com. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.