Karyopharm Drops 40% After FDA Posts Selinexor Meeting Briefing Docs

Shares of Karyopharm (KPTI) are moving sharply lower after the FDA posted briefing documents for the Oncologic Drugs Advisory Committee Meeting planned for February 26 to review the New Drug Application for Selinexor. Selinexor is indicated in combination with dexamethasone for the treatment of patients with relapsed refractory multiple myeloma, or RRMM, who have received at least three prior therapies and whose disease is refractory to at least one proteasome inhibitor (PI), at least one immunomodulatory agent, and an antiCD38 monoclonal antibody.

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In the "Issues" section of the document, FDA staff state: "STORM was a single arm trial evaluating the combination of selinexor and dexamethasone. Given that historical studies have shown response rates of 10-27% to high-dose dexamethasone for RRMM and selinexor did not demonstrate single agent activity in RRMM in the phase 1 trial KCP-330-001, it is difficult to isolate the treatment effect of selinexor...Treatment with selinexor is associated with significant toxicity...As a monotherapy, selinexor yielded only one response in 56 patients with RRMM in the phase 1 dose escalation and expansion study KCP-330-001...The proposed starting dose was not well tolerated in the phase 2 trial given that 88.6% the patients in Part 2 of STORM required at least one dose modification due to a TEAE and 28.5% of patients discontinued treatment with selinexor-dexamethasone due to a TEAE". 

In the "Conclusions" section, the FDA staff wrote: "Given the limited efficacy and significant toxicity demonstrated in this population, it is unclear whether treatment with selinexor-dexamethasone provides a clinically meaningful benefit that outweighs the risks of treatment. The limitations of interpreting safety and efficacy from a single arm trial, and lack of single agent activity of selinexor coupled with historical data showing activity of dexamethasone in RRMM, add to the challenges in interpreting the results of the pivotal study...The RWD analyses of the FHAD population were not prespecified and have major methodological issues. The results of Study KS-50039 are difficult to interpret due to these limitations, and therefore, are not acceptable as supportive evidence for the NDA." Following a trading pause for volatility, Karyopharm shares are down $3.54, or nearly 40%, to $5.43. Reference Link

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