FDA surprises with controversial OK for Karyopharm’s selinexor – US Biotech Karyopharm Therapeutics (Nasdaq:KPTI) saw its stock jump 36% yesterday on news that the FDA has granted an accelerated approval to its anticancer Xpovo (selinexor), a nuclear export inhibitor, for late-line relapsed or refractory multiple myeloma (RRMM). The news surprised many specialist investors as the application was based on a subset of a single arm Phase II study and use of the drug carries significant risks. Indeed, an FDA advisory panel had previously recommended that the US regulator wait for the outcome of the “BOSTON” Phase III study (which is due at the year end, at the earliest) before making any final decision regarding approval (the FDA is not required to follow the advisory committe’s recommendations but ususally does so).
The approival is for use in patients with RRMM who have received at least four prior therapies and whose disease is refractory to at least two proteasome inhibitors, at least two immunomodulatory agents, and an anti-CD38 monoclonal antibody, whereas the BOSTON study tests the drug in patients who have had one to three prior lines of therapy. Karyopharm expects Xpovo to be made available in the US next week at a price of $22,000/month. A marketing application is also currently under review at the European Medicines Agency.
The accelerated approval was based on results from an 83-patient subset of the most advanced patients in the STORM trial, which was itself a single-arm, open-label study of patients with RRMM. STORM Part 2 included 122 patients with RRMM who had previously received three or more anti-myeloma treatment regimens, 83 of which had disease that was documented to be refractory to bortezomib, carfilzomib, lenalidomide, pomalidomide, and daratumumab. The major efficacy outcome measure was overall response rate (ORR) of 25.3% and the benefit-risk ratio appeared to be greater in this more heavily pretreated population than in the overall trial population.