Once weekly selinexor, carfilzomib, and dexamethasone (SKd) in patients with relapsed/refractory multiple myeloma (MM).

Abstract

8530 Background: Selinexor is a novel, first-in-class selective inhibitor of nuclear export (SINE), which blocks exportin 1 (XPO1), forcing the nuclear retention and activation of tumor suppressor proteins. Selinexor in combination with low dose dexamethasone (Sel-dex) was approved by the FDA, based on data from the STORM study wherein Sel-dex induced an overall response rate (ORR) of 26.2% in patients (pts) with refractory MM. We hypothesize that once weekly (QW) SKd may be an active well tolerated regimen and evaluated this combination in a dose escalation/expansion study. Methods: STOMP is a phase 1b/2 study evaluating various doses and enrolled pts with carfilzomib naive relapsed MM. Oral selinexor was dosed QW at 80 or 100 mg. Carfilzomib was dosed QW (on days 1, 8 and 15 of 28-day cycle) at 56 mg/m2 or 70 mg/m2. Dexamethasone was dosed at 40 mg QW. The primary objectives of the study are to assess the maximum tolerated dose (MTD), recommended phase 2 dose (RP2D), as well as explore the efficacy and safety of SKd. Results: As of January 2020, 18 pts were enrolled. Median age was 71 years (range: 50-76). Median number of prior regimens was 4 (range: 1-8). All pts (n = 18) were previously treated with bortezomib and lenalidomide, and 50% and 56% pts were refractory to bortezomib and lenalidomide respectively. Nine (50%) pts received prior pomalidomide treatment and 8 (44%) pts were refractory. Eleven (61%) pts received prior daratumumab treatment and 9 (50%) were refractory. The MTD was selinexor 80 mg QW, carfilzomib 56 mg/m2 QW and dexamethasone 40 mg QW. The ORR and CBR were 72% and 79% respectively with 4 complete responses, 7 very good partial responses, 2 partial responses, and 1 minimal response. Stable disease was observed in 3 pts. With a median follow-up period of 4.7 (1.8-16.3) months, median progression-free survival has not been reached. Common treatment-related adverse events (total, Grade ≥3) were thrombocytopenia (83.3%, 66.7%), nausea (66.7%, 0%), anemia (55.6%, 11.1%), fatigue (50%, 11.1%), anorexia (44%, 5.6%), weight loss (44%, 0%), and neutropenia (33.3%, 11.1%). Conclusions: Once weekly SKd demonstrated an encouraging ORR of 72% in pts with a median of 4 lines of prior therapy. The majority of responses are deep and predominantly CR and VGPR. The combination is well tolerated with no new safety signal, no Grade ≥3 nausea, vomiting, diarrhea, weight loss or anorexia. The side effects are a function of the dose and schedule and can be managed with dose modification and supportive care. Enrolment is ongoing and supports a phase 3 study of SKd. Clinical trial information: NCT02343042 .