On June 1, 2024 Karyopharm Therapeutics Inc. (Nasdaq: KPTI), a commercial-stage pharmaceutical company pioneering novel cancer therapies, reported the presentation of updated exploratory subgroup analyses from the SIENDO study (NCT03555422), in patients with advanced or recurrent TP53 wild-type endometrial cancer at the 2024 American Society of Clinical Oncology (ASCO) (Free ASCO Whitepaper) Annual Meeting (Press release, Karyopharm, JUN 1, 2024, View Source [SID1234643930]). The data were presented in a special ASCO (Free ASCO Whitepaper) plenary series rapid abstract update session on June 1 at 12:30pm CT and simultaneously published in the Gynecologic Oncology Journal.

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The primary analysis of the Phase 3 SIENDO study of selinexor maintenance therapy in advanced or recurrent endometrial cancer showed improvements in median PFS for the intent-to-treat (ITT) population but were not clinically meaningful. However, an exploratory analysis of a pre-specified subgroup of patients with TP53 wild-type endometrial cancer showed a promising efficacy signal.

In the exploratory subgroup analysis, 113 patients with TP53 wild-type advanced/recurrent endometrial cancer were randomized to receive selinexor (n=77) vs placebo (n=36) as maintenance therapy after 1L platinum-based chemotherapy. As of the April 1, 2024 data cut-off date, and a median duration of follow-up of 36.9 months, selinexor-treated patients had a median PFS of 28.4 months compared to 5.2 months for patients receiving placebo. In selinexor-treated patients with TP53 wild-type/pMMR and TP53 wild-type/dMMR endometrial cancer, median PFS was 39.5 months and 13.1 months compared to 4.9 months and 3.7 months in those treated with placebo, respectively. Although immature, preliminary overall survival (OS) in the TP53 wild-type subgroup was promising with a hazard ratio of 0.65; median OS for selinexor has not been reached.

The updated analyses also highlighted findings from a quality-adjusted time without symptoms or toxicity analysis (Q-TWiST) used to assess quality and toxicity-adjusted PFS. The findings showed the restricted mean Q-TWiST for selinexor to be 26 months compared to 15 months for placebo, resulting in a difference of nearly 11 months.

"The approximately 40 months median PFS observed with selinexor in patients whose tumors are both TP53 wild-type and pMMR, coupled with the robust QTWiST analysis, suggests that selinexor may be an optimal maintenance therapy in endometrial cancer," said Reshma Rangwala, MD, PhD, Chief Medical Officer and Head of Research at Karyopharm. "Our ongoing Phase 3 trial will definitively assess these benefits and may lead to a new standard of care in the novel subgroup of patients defined by TP53 wild-type status."

No new safety signals were identified as of the data cut-off date of April 1, 2024. The most common treatment-emergent adverse events (TEAEs) in selinexor treated TP53 wild-type patients were nausea (90%), vomiting (60%) and diarrhea (45%), the majority of which were grades 1-2. The most common reported grade 3-4 TEAEs included neutropenia (20%), nausea (13%), and thrombocytopenia (10%). TEAEs leading to discontinuations were reported in 17% of patients.

"It is exciting to see the emerging data around progression free survival, as well as an encouraging trend in overall survival and the Q-TWiST metric in the TP53 wild-type subgroup analysis from the SIENDO study," said Vicky Makker, MD, Gynecologic Oncologist, Memorial Sloan Kettering Cancer Center. "The long-term follow-up data further reinforce how selinexor could benefit patients with endometrial cancer, including patients with mismatch repair-proficient disease, and add to the growing body of evidence supporting the potential role of selinexor as a maintenance treatment option for patients whose options are limited."

A copy of the presentation from the "ASCO Plenary Series: Rapid Abstract Updates" special session can be accessed under "Publications and Presentations" in the Investor section of the Company’s website, View Source

Selinexor is being evaluated in a global, Phase 3, randomized, double-blind study, EC-042 (XPORT-EC-042; NCT05611931), as a maintenance therapy following systemic therapy in patients with TP53 wild-type advanced or recurrent endometrial cancer. Karyopharm expects to report data from this trial in the first half of 2025.

The following Karyopharm abstracts will also be presented at ASCO (Free ASCO Whitepaper):

Abstract Title

Presentation Type

Abstract #

Session Date/Time

Endometrial Cancer

Phase 3 Dose Selection for Selinexor in TP53wt Endometrial Cancer Based on Exposure-Response Analysis

Poster

5594

June 3, 2024

9:00am – 12:00pm CDT

Myelofibrosis

Phase 3 Randomized Double-Blind Study Evaluating Selinexor, an XPO1 inhibitor, Plus Ruxolitinib in Jaki-Naïve Myelofibrosis

Poster

TPS6594

June 3, 2024

9:00am – 12:00pm CDT

Phase 2 Study Evaluating Selinexor Monotherapy in Patients with Jaki-Naïve Myelofibrosis and Moderate Thrombocytopenia

Poster

TPS6593

June 3, 2024

9:00am – 12:00pm CDT

About the EC-042 Study
EC-042 (XPORT-EC-042; NCT05611931) is a global, Phase 3, randomized, double-blind study evaluating selinexor as a maintenance therapy following systemic therapy in patients with TP53 wild-type advanced or recurrent endometrial cancer. The EC-042 study was initiated in November 2022 and is expected to enroll up to 220 patients who will be randomized 1:1 to receive either a 60 mg, once-weekly, administration of oral selinexor or placebo until disease progression. The primary endpoint of the study is progression free survival (PFS), as assessed by an investigator, with overall survival as a key secondary endpoint. Further, in connection with the EC-042 Study, Karyopharm entered into a global collaboration with Foundation Medicine, Inc. to develop FoundationOneCDx, a tissue-based comprehensive genomic profiling test to identify and enroll patients whose tumors are TP53 wild-type.

About the SIENDO Study
Karyopharm’s evaluation of selinexor to treat patients with TP53 wild-type advanced or recurrent endometrial cancer is supported by data from an exploratory subgroup analysis from its ongoing SIENDO Study, a European Network of Gynaecological Oncological Trial Groups (ENGOT)-led trial in collaboration with the Gynecologic Oncology Group (GOG) Foundation, Inc. The SIENDO Study is a multicenter, randomized, double-blinded Phase 3 study evaluating the efficacy and safety of oral selinexor versus placebo as a front-line maintenance therapy in patients with advanced or recurrent endometrial cancer following at least one prior platinum-based combination chemotherapy treatment (NCT03555422). Participants in this study with advanced or recurrent disease who had a partial response or a complete response after at least 12 weeks of taxane-platinum combination chemotherapy were randomized in a 2:1 manner to receive either maintenance therapy of 80 mg of selinexor or placebo taken once per week, until disease progression. The primary endpoint in the study was PFS from time of randomization until death or disease progression as assessed by an investigator, with the goal of the study demonstrating a HR of 0.6. In the first quarter of 2022, Karyopharm presented top-line data from the SIENDO study, including preliminary exploratory subgroup analyses. Selinexor-treated patients had a median PFS of 5.7 months compared to 3.8 months for patients on placebo in the full trial population, which was not clinically meaningful. There were no new safety signals identified, and a discontinuation rate of 10.5% due to adverse events (AEs). The most common treatment-emergent AEs in the SIENDO study of any grade were: nausea (84%), vomiting (52%), constipation (37%) and thrombocytopenia (37%). The most common grade 3 treatment-emergent AEs were nausea (10%), neutropenia (9%), thrombocytopenia (7%) and asthenia (6%).

About Endometrial Cancer
Endometrial cancer is the most common cancer of the female reproductive organs in the U.S., with approximately 67,880 new cases expected in 2024 leading to nearly 13,250 deaths.1 In 2022, there were approximately 124,874 new cases and 30,272 deaths in Europe from endometrial cancer, while on a global scale there were 420,368 new cases and approximately 97,723 deaths.2 Since 2000, the incidence of new cases and deaths from endometrial cancer have risen.3 Risk factors include obesity, Type 2 diabetes, high-fat diets, use of tamoxifen and oral estrogens, and delayed menopause.4

About XPOVIO (selinexor)
XPOVIO is a first-in-class, oral exportin 1 (XPO1) inhibitor and the first of Karyopharm’s Selective Inhibitor of Nuclear Export (SINE) compounds approved for the treatment of cancer. XPOVIO functions by selectively binding to and inhibiting the nuclear export protein XPO1. XPOVIO is approved in the U.S. and marketed by Karyopharm in multiple oncology indications, including: (i) in combination with Velcade (bortezomib) and dexamethasone (XVd) in adult patients with multiple myeloma who have received at least one prior therapy; (ii) in combination with dexamethasone in adult patients with relapsed or refractory multiple myeloma who have received at least four prior therapies and whose disease is refractory to at least two proteasome inhibitors, at least two immunomodulatory agents, and an anti-CD38 monoclonal antibody; and (iii) in adult patients with relapsed or refractory diffuse large B-cell lymphoma (DLBCL), not otherwise specified, 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-U.S. 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.

Please refer to the local Prescribing Information for full details.

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.

For more information about Karyopharm’s products or clinical trials, please contact the Medical Information department at:

Tel: +1 (888) 209-9326
Email: [email protected]

SELECT IMPORTANT SAFETY INFORMATION
Warnings and Precautions

Thrombocytopenia: Monitor platelet counts throughout treatment. Manage with dose interruption and/or reduction and supportive care.

Neutropenia: Monitor neutrophil counts throughout treatment. Manage with dose interruption and/or reduction and granulocyte colony‐stimulating factors.

Gastrointestinal Toxicity: Nausea, vomiting, diarrhea, anorexia, and weight loss may occur. Provide antiemetic prophylaxis. Manage with dose interruption and/or reduction, antiemetics, and supportive care.

Hyponatremia: Monitor serum sodium levels throughout treatment. Correct for concurrent hyperglycemia and high serum paraprotein levels. Manage with dose interruption, reduction, or discontinuation, and supportive care.

Serious Infection: Monitor for infection and treat promptly.

Neurological Toxicity: Advise patients to refrain from driving and engaging in hazardous occupations or activities until neurological toxicity resolves. Optimize hydration status and concomitant medications to avoid dizziness or mental status changes.

Embryo‐Fetal Toxicity: Can cause fetal harm. Advise females of reproductive potential and males with a female partner of reproductive potential, of the potential risk to a fetus and use of effective contraception.

Cataract: Cataracts may develop or progress. Treatment of cataracts usually requires surgical removal of the cataract.
Adverse Reactions

The most common adverse reactions (≥20%) in patients with multiple myeloma who receive XVd are fatigue, nausea, decreased appetite, diarrhea, peripheral neuropathy, upper respiratory tract infection, decreased weight, cataract and vomiting. Grade 3‐4 laboratory abnormalities (≥10%) are thrombocytopenia, lymphopenia, hypophosphatemia, anemia, hyponatremia and neutropenia. In the BOSTON trial, fatal adverse reactions occurred in 6% of patients within 30 days of last treatment. Serious adverse reactions occurred in 52% of patients. Treatment discontinuation rate due to adverse reactions was 19%.

The most common adverse reactions (≥20%) in patients with multiple myeloma who receive Xd are thrombocytopenia, fatigue, nausea, anemia, decreased appetite, decreased weight, diarrhea, vomiting, hyponatremia, neutropenia, leukopenia, constipation, dyspnea and upper respiratory tract infection. In the STORM trial, fatal adverse reactions occurred in 9% of patients. Serious adverse reactions occurred in 58% of patients. Treatment discontinuation rate due to adverse reactions was 27%.

The most common adverse reactions (incidence ≥20%) in patients with DLBCL, excluding laboratory abnormalities, are fatigue, nausea, diarrhea, appetite decrease, weight decrease, constipation, vomiting, and pyrexia. Grade 3‐4 laboratory abnormalities (≥15%) are thrombocytopenia, lymphopenia, neutropenia, anemia, and hyponatremia. In the SADAL trial, fatal adverse reactions occurred in 3.7% of patients within 30 days, and 5% of patients within 60 days of last treatment; the most frequent fatal adverse reactions was infection (4.5% of patients). Serious adverse reactions occurred in 46% of patients; the most frequent serious adverse reaction was infection (21% of patients). Discontinuation due to adverse reactions occurred in 17% of patients.
Use In Specific Populations
Lactation: Advise not to breastfeed.

For additional product information, including full prescribing information, please visit www.XPOVIO.com.

To report SUSPECTED ADVERSE REACTIONS, contact Karyopharm Therapeutics Inc. at 1‐888‐209‐9326 or FDA at 1‐800‐FDA‐1088 or www.fda.gov/medwatch.