What: Shares of Arrowhead Research Corp. (ARWR -0.92%), a clinical-stage biopharma specializing in RNAi therapeutics, rose by as much as 38% today on tremendous volume.

This dramatic spike in Arrowhead's share price was triggered by a positive clinical update from the company for its experimental hepatitis B treatment, ARC-520, that is currently being studied in an ongoing mid-stage trial.

Per the company's press release, a group of treatment-naive, hepatitis B virus E-antigen positive patients that were given a single 4 mg/kg dose of ARC-520 saw a peak reduction in the hepatitis surface antigen, HBsAg, of 99%. Additionally, patients presently on a standard form of background therapy and treated with the same dosage of ARC-520, exhibited a mean maximal reduction of 92% in circulating HBeAg. 

Put simply, the therapy essentially cleared the signs of an active hepatitis B infection in some cases. These preliminary trial results were disclosed by the company as part of its analyst day being held in New York today. 

So what: According to the World Health Organization, 240 million people globally are chronically infected with hepatitis B, resulting in approximately 650,000 deaths every year. While there are a handful of approved products that are effective at preventing infection, or suppressing the virus in infected patients, a functional cure is presently lacking. Arrowhead is hoping ARC-520 can fill this unmet medical need. 

Now what: We should learn further details of ARC-520's mid-stage study at today's presentation for analysts. Nonetheless, I'm personally content sitting on the sidelines with this speculative biopharma stock for the time being. After all, ARC-520 still has a long road ahead of it before going up for a formal regulatory review.