Parallel Phase II Clinical Trials of Selinexor in Patients With Advanced Thymoma and Thymic Carcinoma

Thymic epithelial tumors (TETs) are rare and include thymomas (T) and thymic carcinomas (TC). Effective treatment options are needed for patients with progressive disease after platinum-based chemotherapy. Preclinical studies demonstrated antitumor activity of selinexor, an inhibitor of the nuclear receptor exportin-1 (XPO1/CRM1), supporting the clinical development of XPO1-targeted therapy for the treatment of TETs. To further assess the safety and efficacy of selinexor in TETs, we conducted two coordinated parallel phase II clinical trials.

This report includes two nearly identical phase II trials, designed to run in parallel, conducted in the United States (NCT03193437) and Europe (Denmark and France; NCT03466827). Analysis was performed on data pooled from both trials. Both trials were nonrandomized, open-label, two-armed phase II trials (arm A: thymoma, arm B: thymic carcinoma) with the same study design. Patients with histologically confirmed, advanced, inoperable TETs who had progressive disease after treatment with at least one platinum-containing chemotherapy regimen were included. In each 4-week cycle, patients received selinexor 60 mg twice weekly for 3 weeks. To improve tolerability, the starting dose was reduced to 40 mg twice weekly during the study. The primary objective was overall response rate (ORR) assessed by Response Evaluation Criteria in Solid Tumors 1.1, with secondary objectives including progression free survival (PFS), overall survival (OS), and adverse events (AEs) assessed per Common Terminology Criteria for Adverse Event version 4.03.

A total of 31 patients were enrolled between the two trials: 16 with T and 15 with TC. The median age was 57 (range: 41-81) years, with 17 men and 14 women. The median number of previous systemic therapies was 2 (range: 1-9). The starting dose was 60 mg twice weekly for 29 patients (93.5%) and 40 mg twice weekly for two patients (6.5%). There was one complete response in the TC group (ORR 6.7%; 95% confidence interval [CI]: 1.2%-29.8%) and two partial responses (ORR 12.5%; 95% CI: 3.5%-36.0%) in the T group. Stable disease as the best response was observed in 11 patients (68.6%) with T and 12 patients (80%) with TC. The median duration of selinexor therapy was 4.5 (range: 0.1-44.3) months. The most common treatment-related adverse events (TRAEs) were nausea (83.8%), vomiting (45.2%), anemia (41.9%), fatigue (38.7%), and asthenia (38.7%). The most common grade 3 or higher TRAEs were anemia (16.1%), thrombocytopenia (12.9%), and asthenia (12.9%). Furthermore, 20 patients (64.5%) required dose reductions due to AEs and 20 patients (64.5%) required dose interruptions. In the T group, the median PFS was 13.6 months (95% CI: 6.3-44.3), and the median OS was not reached. In the TC group, the median PFS was 7.8 months (95% CI: 4.3-15.5) and the median OS was 15.5 months (95% CI: 13.0-29.9). The trials were halted prematurely due to overall low ORRs and budgetary constraints.

Selinexor demonstrated modest anticancer activity in patients with pretreated advanced TETs. The treatment was complicated by high rates of TRAEs, leading to frequent dose reductions and interruptions.