What's Fueling Karyopharm Theraputics Inc's Monster 50% Pop Today?

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 Karyopharm Theraputics Inc are trading over 47% higher this afternoon after topping out at a gain of over 50% at roughly 1 PM today. The development-stage biotech is enjoying a huge influx of positive sentiment following the release of its initial Phase 1 data  for Selinexor.

So what: Selinexor, which is a selective inhibitor of nuclear export designed to treat multiple myeloma, has been part of an eight-patient trial in conjunction with a low dosage of dexamethasone. The company reported a clinical benefit response rate -- a category combining stringent complete responses (one patient), partial responses (three patients), and minor responses (two patients) -- of 75%. All patients had advanced hematological malignancies and had received a median of 5.5 prior rounds of therapy for multiple myeloma, and all but one had received failed stem cell transplants.

Now what: This response rate is promising for such an advanced stage of disease, but it's still very early in the trial process, and the sample size is still very small. This is Karyopharm's single largest daily gain since it went public in late 2013, but the stock has already been quite volatile, as development-stage stocks tend to be. I wouldn't be surprised if the share price falls back to earth between now and the next trial update, and it's the later-stage trials that are more important for Selinexor's success at any rate. Keep your eyes open, but don't dive in just yet.