Material Event (Form 8-K)

On August 31, 2026, Karyopharm Therapeutics Inc. (the "Company") announced that it has submitted a supplemental New Drug Application ("sNDA") to the U.S. Food and Drug Administration ("FDA") seeking Accelerated Approval for XPOVIO^® (selinexor) in combination with ruxolitinib for patients with myelofibrosis. The Company requested Priority Review of the application, which, if granted, could result in a six-month review process. The Company expects to receive notice of the FDA's decision on sNDA filing acceptance and, if accepted, the anticipated review timelines in the fourth quarter of 2026, following the FDA's 60-day filing review period.

Following the topline results of the Phase 3 SENTRY trial, the Company has engaged productively with the FDA. The sNDA submitted is based, in part, on data from the SENTRY trial that the Company believes supports a positive benefit-risk profile for the combination, including a promising signal of overall survival. The Company expects approval under the Accelerated Approval pathway would require the FDA to agree that spleen volume reduction ≥ 35% (SVR35) is a reasonably likely surrogate endpoint to predict overall survival. The Company plans to use long-term overall survival data from the Phase 3 SENTRY trial to verify clinical benefit and support conversion from accelerated to traditional approval and expects to continue working with the FDA during its review of the sNDA to finalize the confirmatory evidence plan.