Vertex Pharmaceuticals (Nasdaq: VRTX) is trading up 15% today after the company released positive phase 3 results for its cystic fibrosis drug, VX-770.

That's a major move. Vertex isn't some podunk drugmaker -- the 14% increase represents a $1.1 billion increase in Vertex's valuation. Investors think the drugless company is now worth nearly $9 billion.

Granted the data on VX-770 looks pretty good. Unlike other antibiotics like Novartis' (NYSE: NVS) Tobi or Gilead Sciences' (Nasdaq: GILD) Caysto, which just treat the symptoms of cystic fibrosis, VX-770 treats the underlying cause. The 10.5% improvement in lung function compared to placebo is pretty remarkable.

But the drug only works in a subset of patients that have a specific mutation that only occurs in 4% of cystic fibrosis patients in the U.S. I have a hard time seeing VX-770 hitting blockbuster status.

That leaves most of the $9 billion valuation to be carried by the company's hepatitis C drug, telaprevir. The drug is another game changer with the ability to drastically increase the cure rate compared to current hepatitis C drugs sold by Roche and Merck (NYSE: MRK) that only cure about half of the patients.

I don't want to root against Vertex; the company is a prototypical Motley Fool Rule Breaker, changing the treatment paradigm in multiple indications. But there are an awful lot of sales already priced into Vertex's valuation.

Vertex will get a decision from the Food and Drug Administration about its marketing application for telaprevir in May. I fully expect an approval, but there's no room for error at these prices. One false step in the approval process or sales ramp up for telaprevir or the second phase 3 trial for VX-770 and investors are going to punish the company.

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Vertex Pharmaceuticals is a Motley Fool Rule Breakers recommendation. Gilead Sciences is a Motley Fool Stock Advisor choice. Novartis is a Motley Fool Global Gains recommendation. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.

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