Vertex Shareholders Stay Vexed

New clinical data from Vertex Pharmaceuticals (VRTX Quote) regarding its hepatitis C drug telaprevir, expected at a medical meeting next month, seem to have investors on edge.

Shares of the Cambridge, Mass.-based biotech firm continue show weakness on worries that telaprevir won't live up to expectations when new phase II data are presented at the European Association for the Study of Liver Disease meeting on April 11-15.

I last wrote about telaprevir in early February with Vertex shares at $35, at the time down from a recent high of $44. On Tuesday, the stock closed up 20 cents at $27.85.

Like then, there doesn't seem to be a specific nugget of negative information about telaprevir forcing Vertex lower (at least not that I've been able to pick up). Instead, there's a general uneasiness -- even confusion -- about the telaprevir data that Vertex will bring to the EASL meeting and how it will be interpreted by hepatitis C experts and investors.

At the risk of coming off a bit too wonky, I want to preview Vertex's upcoming EASL presentation. It may not dispel any fears, but with any hope it will make interpreting next month's data easier.

The most highly anticipated news will come from what is known as "Arm D" of Vertex's Prove 1 study. In this arm, 20 treatment-naive hepatitis C patients (those who have never taken anti-hepatitis C drugs) were given a triple combination of telaprevir plus interferon alpha and ribavirin (the latter two drugs representing the current, standard hepatitis C treatment.) Patients in this arm of the study were treated with all three drugs for 12 weeks, then all treatment was stopped.