Karyopharm Announces Favorable Change in Co-Primary Endpoint for Pivotal Phase 3 SENTRY Trial in Myelofibrosis

Karyopharm Therapeutics Inc. recently announced that, following feedback from the US FDA, it will be replacing TSS50, one of the co-primary endpoints in the Phase 3 SENTRY Trial (NCT04562389) with Abs-TSS. Abs-TSS measures the average improvement in patient symptom scores over 24 weeks relative to the patient’s baseline symptom score.

“There remains a tremendous unmet need in myelofibrosis, as less than half of patients achieve SVR35 with each of the approved JAK inhibitors and many patients eventually stop responding to these treatments,” said Dr. Raajit Rampal, Director of the Center for Hematologic Malignancies and Director of the Myeloproliferative Neoplasms Program at Memorial Sloan Kettering Cancer Center. “The Phase 1 trial, which evaluates the combination of selinexor and ruxolitinib, shows an approximate doubling of SVR35 to nearly 80% compared to historical JAKi monotherapy, and meaningful improvements in Abs-TSS with an average 18.5 point improvement at week 24 compared to baseline. I believe these data are meaningful and impressive and provide a strong rationale for the Phase 3 SENTRY trial.”

Data from the company’s Phase 1 trial, evaluating the combination of selinexor 60mg plus ruxolitinib in JAKi naïve myelofibrosis patients, demonstrated that 79% of patients in the intent to treat population (n=14) achieved SVR35 and an average Abs-TSS improvement of 18.5 points in the efficacy evaluable population (n=9), at week 24 relative to baseline. Acknowledging the small sample size, these data are favorable to historical ruxolitinib monotherapy data which indicates that less than half of patients achieve SVR35 and an Abs-TSS improvement of 11 to 14 points¹.  The safety profile remains consistent and no new safety signals have been identified.

“Our confidence in the success of our Phase 3 SENTRY trial increases based on the change in the co-primary endpoint to Abs-TSS, the increased sample size and the data previously presented from our Phase 1 trial evaluating selinexor plus ruxolitinib in JAKi naïve myelofibrosis patients,” said Reshma Rangwala, MD, PhD, Chief Medical Officer and Head of Research at Karyopharm. “Based upon strong enrollment, we remain on track to report top-line results in the second half of 2025.”

“Improving symptomatic burden for patients with myelofibrosis is an important goal in therapy, directly linking to decreases in morbidity and likely mortality,” said Dr. Ruben Mesa, President of Atrium Health Levine Cancer and Charles L. Spurr, MD Professor of Internal Medicine, Wake Forest University School of Medicine. “I am very encouraged by the benefits reported in Karyopharm’s Phase 1 trial of selinexor combined with standard of care ruxolitinib, especially regarding disease associated symptoms. Additionally, I am grateful that the ongoing Phase 3 trial will use Abs-TSS as a co-primary endpoint, which may better represent the cumulative benefit patients experience on symptom burden.”

Abs-TSS is an accepted measure that has been used in other Phase 3 clinical trials in myelofibrosis to evaluate the benefit/risk of an add-on treatment, such as selinexor, to the current standard of care. The change to Abs-TSS is strongly supported by key leading investigators and patient advocacy organizations, which generally view improvement in Abs-TSS from baseline as a more accurate assessment of symptom improvement in head-to-head clinical trials, such as SENTRY.

“We are vocal advocates for evolving myelofibrosis clinical trial endpoints. Growing data that support a newer outcome measure like Abs-TSS that is also meaningful to patients is very encouraging,” said Kapila Viges, Chief Executive Officer, MPN Research Foundation. “Efforts to develop effective treatments and combination therapies with patients’ goals for care in mind are important. For myelofibrosis patients and their families, options matter.”

SENTRY (NCT04562389) is a pivotal, Phase 3 clinical trial evaluating a once-weekly dose of 60mg of selinexor in combination with twice-daily ruxolitinib versus placebo plus ruxolitinib in JAKi naïve patients with platelet counts >100 x 10⁹/L. Karyopharm intends to enroll approximately 350 JAKi naïve patients with myelofibrosis in this Phase 3 trial; patients are randomized 2-to-1 to the selinexor arm. The co-primary endpoints will be spleen volume response rate ≥ 35% (SVR35) at week 24 and the change in absolute total symptom score (Abs-TSS) over 24 weeks relative to baseline.

XPOVIO is a first-in-class, oral exportin 1 (XPO1) inhibitor and the first of Karyopharm’s Selective Inhibitor of Nuclear Export (SINE) compounds to be approved for the treatment of cancer. XPOVIO functions by selectively binding to and inhibiting the nuclear export protein XPO1. XPOVIO is approved in the US and marketed by Karyopharm in multiple oncology indications, including: (i) in combination with Velcade (bortezomib) and dexamethasone (XVd) in patients with multiple myeloma after at least one prior therapy; (ii) in combination with dexamethasone in patients with heavily pre-treated multiple myeloma; and (iii) in patients with diffuse large B-cell lymphoma (DLBCL), including DLBCL arising from follicular lymphoma, after at least two lines of systemic therapy. XPOVIO (also known as NEXPOVIO in certain countries) has received regulatory approvals in various indications in a growing number of ex-US territories and countries, including but not limited to the European Union, the United Kingdom, China, South Korea, Canada, Israel and Taiwan. XPOVIO and NEXPOVIO is marketed by Karyopharm’s partners, Antengene, Menarini, Neopharm and FORUS in China, South Korea, Singapore, Australia, Hong Kong, Germany, Austria, Israel, and Canada.

Selinexor is also being investigated in several other mid- and late-stage clinical trials across multiple high unmet need cancer indications, including in endometrial cancer and myelofibrosis.

 Karyopharm Therapeutics Inc. (Nasdaq: KPTI) is a commercial-stage pharmaceutical company whose dedication to pioneering novel cancer therapies is fueled by a belief in the extraordinary strength and courage of patients with cancer. Since its founding, Karyopharm has been an industry leader in oral compounds that address nuclear export dysregulation, a fundamental mechanism of oncogenesis. Karyopharm’s lead compound and first-in-class, oral exportin 1 (XPO1) inhibitor, XPOVIO (selinexor), is approved in the US and marketed by the company in three oncology indications. It has also received regulatory approvals in various indications in a growing number of ex-US territories and countries, including Europe and the United Kingdom (as NEXPOVIO) and China. Karyopharm has a focused pipeline targeting indications in multiple high unmet need cancers, including in multiple myeloma, endometrial cancer, myelofibrosis, and diffuse large B-cell lymphoma (DLBCL). For more information,  visit www.karyopharm.com.