KPTI Selinexor + Ruxolitinib sNDA for Myelofibrosis

Karyopharm Therapeutics (KPTI) submitted a supplemental New Drug Application (sNDA) on August 31 seeking accelerated approval of selinexor (XPOVIO) in combination with ruxolitinib (Jakafi) for JAK-inhibitor-naive myelofibrosis, and it requested Priority Review. The stock trades near $1.87, leaving the commercial-stage oncology company at microcap levels as it bets the filing becomes a catalyst.

The submission rests on the Phase 3 SENTRY trial, which randomized 353 patients to selinexor plus ruxolitinib or placebo plus ruxolitinib. The combination nearly doubled the share of patients reaching SVR35 (at least a 35% reduction in spleen volume) at week 24, a measure the FDA has agreed is a reasonably likely surrogate for overall survival, and showed a promising early overall-survival signal. Spleen shrinkage matters in myelofibrosis because an enlarged spleen drives the pain, fatigue, and early satiety patients describe.

Myelofibrosis is a JAK-inhibitor-only market today. Ruxolitinib and its peers dominate, and no combination or non-JAK mechanism is approved. The trial enrolled patients who had not yet taken a JAK inhibitor, so the filing targets the frontline setting where most patients start treatment. If cleared, selinexor plus ruxolitinib would be the first approved combination and the first XPO1 inhibitor in the disease. Selinexor blocks XPO1, a nuclear export protein that shuttles tumor-suppressor proteins out of the cell nucleus; trapping those proteins inside restores their tumor-suppressing work. It is an oral pill, a contrast to infused regimens, and it already sells as XPOVIO in multiple myeloma and diffuse large B-cell lymphoma, so Karyopharm is extending an approved molecule rather than launching a new one.

The catch is real. Accelerated approval depends on confirmatory overall-survival data still maturing, Priority Review is requested but not granted, and Karyopharm will not learn whether the FDA even accepted the filing until the fourth quarter, after the 60-day filing review. If Priority Review is granted, the PDUFA clock runs roughly six months from acceptance, putting a decision in the first half of 2027.

The submission converts the plan Karyopharm announced in July into a concrete filing, as outlined in the selinexor and ruxolitinib sNDA plan. It also refocuses the pipeline after selinexor failed a Phase 3 endometrial cancer trial earlier this month. Karyopharm has held Fast Track designation for selinexor in myelofibrosis since July 2023, and management has called the US opportunity multi-billion-dollar. Read the announcement here.

What to watch next: the FDA’s filing-acceptance decision in Q4 2026, which starts the PDUFA clock if Priority Review is granted.