KPTI Files Selinexor Plus Ruxolitinib sNDA in Myelofibrosis

Karyopharm Therapeutics (KPTI) announced on July 30 that it planned to submit a supplemental New Drug Application to the FDA in August 2026 seeking accelerated approval of selinexor in combination with ruxolitinib for myelofibrosis. The company followed through: Karyopharm submitted the sNDA on August 31, 2026, and requested Priority Review. If approved, it would be the first combination therapy for the disease to incorporate a drug class beyond JAK inhibitors.

Selinexor is an oral XPO1 inhibitor already approved for multiple myeloma and diffuse large B-cell lymphoma, marketed as Xpovio. XPO1 is a nuclear export protein that shuttles tumor suppressor proteins out of the cell nucleus. By blocking XPO1, selinexor traps those proteins inside the nucleus, restoring their tumor-suppressing function. In myelofibrosis, a rare bone marrow cancer, the drug pairs a novel mechanism with the standard JAK inhibitor ruxolitinib, attacking the disease through two distinct pathways.

The sNDA is based on the Phase 3 SENTRY trial (NCT04562389, N=353), which randomized JAK inhibitor-naive myelofibrosis patients with platelet counts above 100 x 10^9/L to selinexor 60 mg once weekly plus ruxolitinib or placebo plus ruxolitinib. The trial met its first co-primary endpoint: SVR35 at week 24 was achieved in 49.8% of the combination arm versus 28.0% for ruxolitinib alone (odds ratio 2.58, 95% CI 1.60–4.17, p<0.0001). The combination nearly doubled spleen response rates. The FDA agreed in writing that SVR35 qualifies as a reasonably likely surrogate endpoint for accelerated approval, which is the regulatory pathway Karyopharm is pursuing.

SENTRY also showed an overall survival signal at topline: HR 0.43 (95% CI 0.19–1.00, nominal one-sided p=0.022), with Kaplan-Meier curves separating around month 9. The combination also produced reductions in variant allele frequency, suggesting it may modify the underlying disease rather than just control symptoms. Grade 3 or higher treatment-emergent adverse events occurred in 70% of the combination arm versus 50% for ruxolitinib alone, and 15% of combination patients discontinued due to adverse events versus 9% on placebo. The trial has no crossover provision and remains blinded during ongoing follow-up, preserving the integrity of the confirmatory OS data Karyopharm will need to verify clinical benefit post-approval.

Karyopharm trades at $1.92 with a market cap near $159 million. The filing comes the same week the company reported that its Phase 3 XPORT-EC-042 trial of selinexor in endometrial cancer maintenance missed its primary endpoint, narrowing the company’s near-term pipeline to the myelofibrosis program. Analysts have cut targets aggressively, with HC Wainwright reducing from $13 to $3 and Piper Sandler from $16 to $7.

Myelofibrosis is currently treated exclusively with JAK inhibitors: ruxolitinib (Incyte’s Jakafi), fedratinib, pacritinib, and momelotinib. All four share the same mechanism. Selinexor would add a first-in-class XPO1 inhibitor to the treatment arsenal, and Karyopharm will request Priority Review, which if granted would put a PDUFA date roughly six months after FDA receipt, placing a decision in early-to-mid 2027. The data was presented at ASCO 2026 and published in the Journal of Clinical Oncology.

The risk is straightforward: the FDA could require mature overall survival data before approval, which would push a decision well beyond 2027. The sNDA leans on a surrogate endpoint and a promising but immature OS signal. If the FDA accepts the filing with Priority Review, the stock re-rates on the path to a 2027 decision. If not, the wait extends.

What to watch next: the sNDA submission confirmation and whether the FDA grants Priority Review. Update (September 1): Karyopharm submitted the sNDA on August 31, 2026, and requested Priority Review. The next catalyst is the FDA’s 60-day filing review — whether the application is accepted and whether Priority Review is granted, expected in Q4 2026. That single designation determines whether Karyopharm gets a 6-month or 10-month review window, and it is the company’s only near-term catalyst. If Priority Review is granted, the PDUFA clock runs roughly six months from acceptance, placing a decision in the first half of 2027.

Source: Karyopharm sNDA myelofibrosis press release | SENTRY trial on ClinicalTrials.gov (NCT04562389)