Carl Icahn's Securities and Exchange Commission filing for the second quarter came out this week, but it pretty much looked like the previous quarter in the biotech sector.

The billionaire investor ditched his investment in Adventrx Pharmaceuticals, but is still holding on to Biogen Idec (Nasdaq: BIIB), Genzyme (Nasdaq: GENZ) and Amylin Pharmaceuticals (Nasdaq: AMLN), three drugmakers that are off their multi-year highs but have the potential to turn things around. The big question is whether you should follow suit.

New leader! Better results?
Whether it happened that way or not, it sure looks like Icahn's pestering finally pushed Biogen's old CEO James Mullen into retirement. The new guy, George Scangos, had been focused on development of new drugs as CEO of Exelixis (Nasdaq: EXEL), a development-stage drugmaker.

The potential change in focus could help Biogen's pipeline, but the company's near-term future lies in its already-approved multiple sclerosis drug, Tysabri. Biogen and marketing partner Elan (NYSE: ELN) need to figure out a way to convince patients that the rewards are worth the risks. Considering that the risks include dying from a brain infection, that's no easy task.

An acquisition play. Or maybe not
The rumors surrounding a potential purchase of Genzyme by sanofi-aventis have died down considerably. Shares have slumped a little, although they're still much higher than they were before The Wall Street Journal broke the news.

I recommended holding off on buying shares a few weeks ago, and that would still be my recommendation today. There's no reason to think that the two aren't still talking about marriage, but there's also no way to know if a deal will definitely get done; Sanofi shouldn't be willing to overpay and Genzyme may not be willing to take less.

Without a buyout, Genzyme's shares may fall back to their pre-rumor state until management can show that it can turn Genzyme's manufacturing woes around.

Waiting to exhale
Sales of Amylin's diabetes drug Byetta have fallen and taken Amylin's stock with it, but all that could change in October when the Food and Drug Administration is set to make a decision about Bydureon, the once-weekly version of Byetta.

Amylin and marketing partner Eli Lilly (NYSE: LLY) should have an easier time selling Bydureon compared to the current twice-daily version. With just 52 shots a year, the drug might even be able to compete with oral medications that have to be taken daily.

Of Ican's three biotechs, Amylin has the clearest path to recovery, but it isn't without risk either. The FDA turned down the approval of Bydureon once already citing, among other things, "clarification of existing manufacturing processes." Bydureon uses an extended release technology developed by Alkermes (Nasdaq: ALKS), and the FDA will want to make sure that the manufacturing is reproducible between manufacturing lots.

Icahn is in control. Are you?
As much as I'm not a fan of Icahn's activist activities that sometimes seem more focused on short-term gains than the long-term health of the company, there's no doubt that he picks his spots carefully and is fully in control of his emotions. You can't fall in love with a biotech and I imagine he's holding on to these three because he thinks they have the ability to turn around.

Icahn also has a little more power than the average investor because he controls board seats on all three companies. In the case of Genzyme, that might actually prevent him from selling if he's privy to inside information about buyout offers, but the seats also give him some control over how each company proceeds.

The average investor will just have to put their faith in managements' ability to lead the companies out of their current doldrums. If you can't do that, following Icahn might not be such a great idea.

Hypergrowth stocks may be overvalued, but that doesn't mean you should short them either argues Tim Hanson.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool owns shares of Exelixis and has a disclosure policy.