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1996 Efficacy and Safety of Selinexor, Pomalidomide, and Dexamethasone (SPd) for Treatment of Patients with Relapsed or Refractory Multiple Myeloma (RRMM)

Program: Oral and Poster Abstracts
Session: 654. Multiple Myeloma: Pharmacologic Therapies: Poster I
Hematology Disease Topics & Pathways:
Research, Clinical trials, Combination therapy, Clinical Research, Treatment Considerations
Saturday, December 7, 2024, 5:30 PM-7:30 PM

Muhamed Baljevic, MD1, Nizar J. Bahlis, MD2, Rami Kotb, MD3, Gary J. Schiller, MD4, Brea Lipe, MD5, Sumit Madan, MD6, Heather J. Sutherland, MD, PhD, FRCPC7, Suzanne Lentzsch, MD, PhD8, Natalie Callander, MD9, Noa Biran, MD10, Dane Van Domelen11*, Tomer Mark11* and Darrell White, MD, MSc12

1Vanderbilt University Medical Center, Nashville, TN
2University of Calgary, Charbonneau Cancer Research Institute, Calgary, AB, Canada
3Cancer Care Manitoba, Winnipeg, MB, Canada
4David Geffen School of Medicine, University of California, Los Angeles, CA
5University of Rochester, Rochester, NY
6Banner MD Anderson Cancer Center, Gilbert, AZ
7Vancouver General Hospital, Vancouver, BC, Canada
8Columbia University, New York, NY
9University of Wisconsin, Carbone Cancer Center, Madison, WI
10Hackensack University Medical Center, Hackensack, NJ
11Karyopharm Therapeutics, Newton, MA
12Queen Elizabeth II Health Sciences Centre and Dalhousie University, Halifax, NS, Canada

Introduction: Multiple myeloma (MM) remains incurable; despite the promise of T-cell engaging therapies, no standard of care has been established for patients with RRMM after prior treatment with immunomodulatory agents (IMiDs), proteasome inhibitors (PIs), or anti-CD38 monoclonal antibodies (αCD38). Large observational studies, such as LocoMMotion, have reported short median progression free survival (mPFS) of approximately 4.5 months in triple-class–exposed (TCE) RRMM with commonly used anti-MM agents; however, the vast majority of these patients did not receive selinexor treatment. Selinexor, an oral exportin 1 (XPO1) inhibitor approved in combination with dexamethasone (d) in penta-refractory MM and with d and bortezomib in RRMM after ≥1 prior therapy, is being evaluated with pomalidomide (P) and d (SPd) for the treatment of RRMM in the Phase 1b/2 STOMP trial (NCT02343042). Updated clinical and safety data for the cohorts that received SPd regimens with 40 mg or 60 mg once weekly (QW) selinexor are presented.

Methods: The SPd arm of the multi-arm STOMP study evaluated selinexor at multiple doses and schedules in combination with Pd (P doses tested consisted of 2 mg, 3 mg, or 4 mg QD) in patients with RRMM. Study objectives were to determine the maximum tolerated dose and the recommended Phase 2 dose to assess safety and to examine the efficacy of the SPd regimen. Response assessments were investigator-determined per International Myeloma Working Group criteria.

Results:

Patient Demographics

As of March 25, 2024, 81 patients had been enrolled in the SPd arm, including 20 in the 60 mg QW (SPd60) and 16 in the 40 mg QW (SPd40) groups. Of all patients treated with SPd, 53.1% were male, the median age was 65, and patients had a median 3 prior lines of therapy. Percentage of patients with prior exposure/refractory status to IMiD was 100%/86.4%; PI 100%/80.2%, αCD38 33.3%/30.9%, and TCE: 33.3%/25.9%.

Efficacy

The investigator-assessed overall response rate (ORR) was 39.5% (95% CI 28.8, 51.0) for the entire cohort, 55.0% (95% CI 31.5, 76.9) for SPd60, and 43.8% (95% CI 19.8, 70.1) for SPd40. The very good partial response or better rate was 19.8% (95% CI 11.7, 30.1) in the entire cohort, 30.0% (95% CI 11.9, 54.3) in SPd60, and 31.3% (95% CI 11.0, 58.7) in SPd40. There were 2 stringent complete responses (CRs; 1 in SPd60 and 1 in SPd40, both TCE) and 1 CR (SPd40). For the entire cohort, the median time to response was 1.1 months (95% CI 1.0, 2.0).

Updated PFS and duration of response results will be presented.

Safety

The most common treatment emergent adverse events (TEAEs) were:

Neutropenia

  • Entire cohort: 67.9% any grade/60.5% G3-4
  • SPd60: 75.0%/60.0%
  • SPd40: 68.8%/68.8%

Fatigue

  • Entire cohort: 64.2%/13.6%
  • SPd60: 75.0%/15.0%
  • SPd40: 62.5%/6.3%

Nausea

  • Entire cohort: 61.7%/1.2%
  • SPd60: 70.0%/0
  • SPd40: 50.0%/0

Anemia

  • Entire cohort: 54.3%/33.3%
  • SPd60: 65.0%/25.0%
  • SPd40: 31.3%/18.8%

Thrombocytopenia

  • Entire cohort: 49.4%/29.6%
  • SPd60: 45.0%/25.0%
  • SPd40: 25.0%/18.8%

Median duration of exposure in weeks was 19.0 (range 1, 260) in the entire cohort, 22.0 (7, 114) in SPd60, and 28.0 (4, 176) in SPd40. Median relative selinexor dose intensity was 86.4% (57.5 mg/week) for the entire cohort, 77.5% (46.5 mg/week) for SPd60, and 93.2% (37.3 mg/week) for SPd40.

Conclusions: The all-oral combination of SPd showed signs of preliminary efficacy and was generally tolerable in patients with RRMM. Although the ORR was greater in the SPd60 cohort, TEAEs were less frequent, duration of exposure was longer, and higher dose intensity was achieved for patients treated with SPd40. These data support the further evaluation of low-dose weekly selinexor in the ongoing EMN29 trial (NCT05028348) of SPd40 versus elotuzumab and Pd in TCE RRMM progressing immediately after a αCD38-containing line of therapy.

Disclosures: Baljevic: Janssen Biotech, BMS/Celgene, Sanofi-Genzyme: Other: advisory board; AbbVie, Pfizer: Consultancy; Parexel: Other: IRC. Bahlis: Pfizer, Janssen: Research Funding; AbbVie, Amgen, BMS, Celgene, Janssen, GSK, Genentech, Karyopharm, Kyte, Novartis, Pfizer, Roche, Sanofi, Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Kotb: Karyopharm.: Current holder of stock options in a privately-held company; Akcea, Amgen, Bristol Myers Squibb, Celgene, Janssen, Merck, Pfizer, Sanofi, Takeda: Honoraria; Merck, Sanofi: Research Funding. Lipe: Janssen and amgen: Research Funding; Janssen, karyopharm, bms, Sanofi, Pfizer, and abbvie: Consultancy, Honoraria. Madan: Harpoon, Karyopharm: Other: Travel, accommodations, expenses; Karyopharm, Sanofi, Pfizer, Janssen: Consultancy; Karyopharm, Harpoon, Pfizer, Iteos: Research Funding. Sutherland: Sanofi: Consultancy; Celgene: Consultancy; Amgen: Consultancy; GSK: Research Funding; Karyopharm: Research Funding; Janssen: Consultancy, Research Funding. Lentzsch: Caelum Bioscience: Patents & Royalties; Pfizer, Regeneron, Janssen, GSK, Sanofi, BMS, Karyopharm, Antigia: Consultancy, Membership on an entity's Board of Directors or advisory committees; PeerView, Clinical Care, Options (CCO), RedMed, Aptitude, Bio Ascend: Speakers Bureau. Biran: Amgen: Research Funding; AbbVie: Consultancy; Karyopharm: Research Funding; Bristol Myers Squibb: Consultancy, Honoraria, Research Funding, Speakers Bureau; Janssen: Consultancy, Honoraria, Research Funding, Speakers Bureau; Sanofi: Honoraria, Speakers Bureau; Pfizer: Consultancy, Honoraria. Van Domelen: Karyopharm Therapeutics: Current Employment. Mark: Karyopharm Therapeutics: Current Employment. White: GSK: Honoraria; Pfizer: Honoraria; Sanofi: Honoraria; Karyopharm: Honoraria; Janssen: Honoraria; Forus: Honoraria; BMS: Honoraria; Antengene: Honoraria; Amgen: Honoraria.

OffLabel Disclosure: Selinexor approved in combination with dexamethasone (d) in penta-refractory MM and with d + bortezomib in relapsing/refractory MM (RRMM) after ≥1 prior therapy

*signifies non-member of ASH