Overall survival (OS) with oral selinexor plus low dose dexamethasone (Sd) in patients with triple class refractory-multiple myeloma (TCR-MM).

8014 Background: TCR-MM is defined as being refractory to immunomodulatory agents, proteasome inhibitors, and anti-CD38 mAbs, representing an urgent unmet medical need with a median OS of 3-5 months( Pick M et al, Eur J Haem 2018; Gandhi U et al, ASH 2018). Sd has shown a 26.2% overall response rate (ORR) in 122 patients (pts) with TCR-MM in the Phase 2b STORM study ( Chari A et al, ASH 2018). Here, we evaluate the OS of pts in the STORM study with Sd and in pts with bortezomib, carfilzomib, lenalidomide, pomalidomide, and daratumumab (“penta”)-exposed, TCR-MM from an observational cohort not receiving Sd. Methods: Data were drawn from STORM and a retrospective cohort from the nationally representative Flatiron Health Analytic Database (FHAD). All pts from both sources had penta-exposed TCR-MM. In order to align study populations, OS was evaluated in pts in STORM whose first therapy after their MM reached TCR status was Sd and in pts in the FHAD who received ≥1 therapy after their MM reached TCR status. The index date for this evaluation was the start date of treatment after their MM reached TCR status. A Cox proportional hazards regression model was performed to assess the survival impact of Sd. In STORM, ORR was assessed by an Independent Review Committee based on IMWG criteria. Results: In the FHAD, 69 pts with TCR-MM were identified. Characteristics of the two groups of pts were similar, except that pts in STORM were more heavily pretreated, had a higher frequency of high-risk MM, a longer time since initial diagnosis of MM, and higher baseline hemoglobin and platelet values. Among the 122 pts in STORM, 64 received Sd as their first therapy after their MM became TCR, and ORR was 32.8%. Among the 69 pts from FHAD, 37 received ≥1 therapy after their MM became TCR. Median OS (N = 64) was 10.4 months for pts receiving Sd in STORM and 5.2 months (N = 37) for pts not receiving Sd in FHAD (HR = 0.49, p = 0.0241). Conclusions: The prognosis of TCR-MM in the real-world population appears very poor. Within the limits of this analysis, median OS of pts receiving Sd as their first therapy after their MM becomes TCR is significantly better than those not receiving Sd, suggesting that Sd may be associated with an OS benefit in pts with TCR-MM. Clinical trial information: NCT02336815.