When a drugmaker increases the odds that its pivotal study will produce positive results, the markets are bound to react positively. But when a study could get that drugmaker's billion-dollar blockbuster lead drug onto the market years sooner, and the odds of that result go up, shares of the company are bound to skyrocket. That has been the case for Vertex Pharmaceuticals (Nasdaq: VRTX) over the past two days.

On Monday, Vertex released an abstract of data from a trial testing its anti-hepatitis C virus compound, telaprevir, that showed the drug is effective in patients who previously failed other therapies. Big deal? Definitely, because telaprevir is currently being tested in a phase 2 study called PROVE-3 in patients who have not responded to previous treatments.

In the just-released study results from an open-label phase 2 trial, 26 of 32 hepatitis C patients (81%) treated with Vertex's telaprevir experienced what is known as a rapid virologic response (RVR), otherwise known as no evidence of the hepatitis C virus after four weeks of treatment. Equally as important, while the number of patients who end up being declared cured of their hepatitis C virus is almost always lower than the RVR rate, RVR rates are an excellent predictor of who will go on to be cured of the disease.

Vertex and partner Johnson & Johnson's (NYSE: JNJ) telaprevir has produced this sort of efficacy data in small studies before, but these are some of the first study results for the drug in patients who failed to respond to interferons, which are the gold standard for treating HCV today. Any drug is bound to be a success if it can substantially help the 50% or so of patients who fail to clear their HCV virus after treatment with an interferon.

As I've stated before, if telaprevir can approach even a 30% cure rate (sustained virologic response) in the PROVE-3 study (and if the PROVE-3's RVR rate is anything like the 80% presented this week, it will), then I wouldn't be surprised to see the FDA approve telaprevir for marketing in some patient groups just based on the PROVE-3 phase 2 data. This could happen because current therapies like Roche's Pegasys and Schering-Plough's (NYSE: SGP) Peg-Intron only produced up to 16% and 14% cure rates in treatment-experienced patients.

Vertex has been on a bit of a roll in the last few days after disappointing investors earlier in the year regarding the prospects for telaprevir. The first PROVE-3 interim data is expected in May of this year, so it won't be long until we get to see if exciting efficacy results like these can be repeated in the PROVE-3 study.

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Fool contributor Brian Lawler does not own shares of any company mentioned in this article. The Fool has an A+ disclosure policy.