Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Achillion Pharmaceuticals (NASDAQ:ACHN), a clinical-stage biopharmaceutical company focused on developing therapies to treat hepatitis C, vaulted higher by as much as 21% after reporting positive data from an eight-week midstage study involving the combination of ACH-3102 and Gilead Sciences (NASDAQ:GILD) Sovaldi for genotype one patients.

Source: Achillion Pharmaceuticals.

So what: According to Achillion's early morning press release, the company's NS5A inhibitor, ACH-3102, when combined with Sovaldi over eight weeks, and without a ribavirin (which has been shown over the years to have its own unpleasant side effects), delivered a sustained virologic response in 100% of the 12 patients tested four weeks after treatment. Achillion plans on testing an additional 12 patients over a six-week, once-daily, treatment course of ACH-3102 and Sovaldi, and reporting its findings before year's end. Achillion also notes that ACH-3102 appeared safe and well-tolerated.

Now what: This is an important step for Achillion Pharmaceuticals because Gilead's Sovaldi is already on pharmacy shelves and racking up billions in sales, while AbbVie's (NYSE:ABBV) direct-acting antiviral combo is under review and on pace for a possible approval given its impressive clinical efficacy. Achillion needs to play catch-up as quickly as possible, and 100% SVR is certainly one way to open Wall Street and the medical community's eyes.

However, a few things to keep in context here. The studies conducted by Gilead and AbbVie that merited Sovaldi's approval and a new drug application from AbbVie were much larger than 12 patients. Obviously Achillion is going to need to run larger-scale phase three studies to demonstrate efficacy before the Food and Drug Administration would even consider an approval, but keep the size of this successful trial in mind as you wrap your hands around an appropriate valuation for Achillion.

Also, keep Achillion's development history in focus. It hasn't been able to move any compounds within its pipeline beyond phase two up until this point, so investors should be considering whether it has the funding and expertise to mount a successful large-scale phase three campaign and, assuming good results, the know-how to market an approved therapy.