Efficacy and safety of pralsetinib in Chinese advanced RET-mutant medullary thyroid cancer patients.

Pralsetinib has demonstrated efficacious activity in various solid tumors, including medullary thyroid cancer (MTC), as observed in the phase 1/2 global ARROW study (BLU-667-1101; NCT03037385). We evaluated the safety and efficacy of pralsetinib in Chinese patients with advanced RET-mutant MTC. In the extension cohort of ARROW, adult patients with advanced MTC, who had not received systemic therapy (except for cytotoxic chemotherapy), were treated with pralsetinib (400 mg once daily, orally). The primary endpoints were blinded independent central-reviewed (BICR) objective response rate (ORR) and safety. Between October 9, 2019, and April 29, 2020, 34 patients were enrolled at 12 centers across China. Among them, 28 patients tested positive for RET mutations in the central laboratory, and 26 of these, with measurable disease at baseline per BICR, were included in the analysis set for tumor response. As of April 12, 2021 (data cutoff), the ORR was 73.1% (95% CI: 52.2-88.4), and the median duration of response was not reached. The most common (≥15%) grade ≥3 treatment-related adverse events (TRAEs) in the 28 patients with RET-mutant MTC were neutrophil count decreased (8/28, 28.6%), blood creatine phosphokinase increased (6/28, 21.4%), and lymphocyte count decreased (5/28, 17.9%). Serious TRAEs were reported by six patients (21.4%), with the most common event being pneumonia (3/28, 10.7%). No patient discontinued treatment or died from pralsetinib-related adverse events. Pralsetinib demonstrated broad, deep, and durable efficacy, as well as a manageable and acceptable safety profile in Chinese patients with advanced RET-mutant MTC.