What happened

Shares of Karyopharm Therapeutics (NASDAQ:KPTI), a clinical-stage biopharmaceutical business focused on oncology, spiked 36% on as of 3:35 p.m. EDT on Wednesday, on heavy trading volume. The enthusiasm can be traced to the approval by the Food and Drug Administration of its lead product candidate.

So what

Karyopharm announced that the FDA has officially given the thumbs-up to selinexor -- now known as Xpovio -- as a treatment for the blood cancer multiple myeloma. Xpovio is the first and only nuclear export inhibitor that has won regulatory approval.

Xpovio is approved to treat adult patients with relapsed or refractory multiple myeloma who have received at least four prior therapies and who meet a few other criteria. The drug must also be used in combination with dexamethasone.

Doctor giving the thumbs-up sign

Traders are cheering the regulatory thumbs-up. Image source: Getty Images.

Now what

The FDA's decision to approve selinexor will likely come as a shock to many investors who've been following this company closely. In February an independent advisory panel voted 8 to 5 in favor of pausing selinexor's review until the results from an ongoing phase 3 study become available in the back half of this year. The agency even announced that it was going to delay its target decision date for the drug from April 6 to July 6, which usually isn't a good sign.

None of that matters now that the FDA has officially given the drug the go-ahead. Bulls who've held throughout the roller-coaster ride certainly deserve to cheer and take a victory lap today.