A 5.3-month improvement in median progression-free survival sounds clinically meaningful until the statistics refuse to cooperate: Karyopharm’s Phase 3 XPORT-EC-042 trial produced a hazard ratio of 0.76 for selinexor versus placebo in TP53 wild-type advanced or recurrent endometrial cancer, but the one-sided p-value landed at 0.0791, just outside the threshold needed to declare success. The gap between the biological signal and the statistical verdict is the entire tension in this story. Patients in the modified intent-to-treat population receiving oral selinexor once weekly had a median PFS of 12.75 months compared to 7.43 months on placebo, a difference investigators describe as clinically meaningful even as the trial formally fails.
The design choices matter here. XPORT-EC-042 enrolled 236 patients in the mITT population and required sequential testing through two populations, with only 106 PFS events observed at the data cut. That event count, relatively modest for a Phase 3 superiority trial, almost certainly contributed to the confidence interval that stretched from 0.51 to 1.12 and swallowed the null. The pMMR subset is the strategic heart of the problem: checkpoint inhibitors such as lenvatinib plus pembrolizumab have demonstrated benefit across endometrial cancer populations, but the magnitude of benefit is demonstrably smaller in pMMR tumors than in dMMR tumors, precisely the patient group selinexor was targeting. Enrolling a population with attenuated response to existing immunotherapy combinations is a rational biomarker strategy, but it also produces a narrower, harder-to-power trial.
Karyopharm is not sitting with the data quietly. The company will continue following patients for overall survival, a key secondary endpoint, and plans a full presentation at a future medical meeting. But the resource allocation signal is unambiguous: investment in endometrial cancer is being reduced, and the company is explicitly pivoting toward its myelofibrosis program, including an sNDA submission and topline data from the 60 mg cohort of SENTRY-2, both anticipated in the second half of 2026. Selinexor already carries FDA approvals in multiple myeloma and other hematologic malignancies, and that commercial base gives Karyopharm the runway to selectively deprioritize a trial that delivered a trend rather than a win.
The one result worth watching closely is overall survival in the XPORT-EC-042 mITT population. A 5.3-month PFS gap that failed statistical thresholds could still translate into a survival separation as follow-up matures, particularly in a pMMR population where post-progression treatment options are constrained. If OS data eventually cross significance, the conversation about XPO1 inhibition in endometrial cancer reopens on very different terms.
Jon Napitupulu is Director of Media Relations at The Clinical Trial Vanguard. Jon, a computer data scientist, focuses on the latest clinical trial industry news and trends.
