Phase 1b study of selinexor, a first-in-class selective inhibitor of nuclear export (SINE) compound, in combination with doxorubicin in patients (pts) with locally advanced or metastatic soft tissue sarcoma (STS).

Abstract

3123 Background: Selinexor is a first-in-class SINE compound with single-agent activity in STS. We undertook this study to determine the safety, tolerability and efficacy of selinexor in combination with doxorubicin in pts with incurable STS. Methods: This phase 1b study was conducted using a bayesian model (modified toxicity probability index). Patients with locally advanced or metastatic STS received selinexor at either 60 or 80mg weekly PO plus doxorubicin (75mg/m2 IV q21 days, max 6 cycles). Pts with stable disease (SD) or better (per RECIST 1.1 criteria) after 6 cycles of combination treatment received selinexor monotherapy until disease progression or unacceptable toxicity. Disease assessments were made with standard imaging after every 2 cycles. Results: 24 pts (19F/5M, ECOG 0/1: 12/12, median age 58.5 years [range 34-74]) were enrolled. Disease subtypes included leiomyosarcoma (n = 6), malignant peripheral nerve sheath tumor (n = 3) and other sarcomas (n = 15). Three pts at 60mg selinexor and 21 pts at 80mg selinexor were treated. The most common G3 drug related adverse events were hematological, neutropenia n = 13 (54%), anemia n = 6 (25%). There were 4 dose-limiting toxicities (2 febrile neutropenia, 1 vomiting and 1 unresolved fatigue) all at the 80mg dose level, but does not satisfy criteria for maximum tolerated dose. Two patients had clinically significant and relevant drop in ejection fraction, presenting with cardiac symptoms. Of the 24 evaluable pts 4 (17%) had a partial response, 16 (67%) had SD as best response and SD > 16 weeks was seen in 13 pts (54%). PK analysis of selinexor did not demonstrate changes compared to single agent profile. The estimated median PFS and OS are 5.5 (95% CI:4.1-7.0) and 9.4 (6.6-13.8) months. Conclusions: Our initial data demonstrate that the combination of selinexor at 80mg with doxorubicin is tolerable and is associated with clinical benefit. Longer term follow up of available patients will be needed to understand toxicity profile. Clinical trial information: NCT03042819.