Larotrectinib in TRK fusion differentiated thyroid carcinoma: updated trial data

Larotrectinib is a first-in-class, highly selective, central nervous system-active tropomyosin receptor kinase (TRK) inhibitor approved for tumour-agnostic use in TRK fusion cancer. It has previously demonstrated rapid and durable disease control and favourable safety in patients with advanced TRK fusion thyroid carcinoma (TC). After an additional 4 years of follow-up with the inclusion of two additional patients, and utilising an independent review committee (IRC) to assess overall response rate (ORR), we report updated pooled analyses from three phase 1-2 larotrectinib clinical trials, focusing only on patients with TRK fusion differentiated TC (DTC). The primary endpoint was the IRC-determined ORR per RECIST v1.1. Duration of response (DoR), progression-free survival (PFS), overall survival (OS) and safety were also assessed. Twenty-four patients (papillary TC, n = 21; follicular TC, n = 2; poorly DTC, n = 1) were included (data cut-off: 20 July 2024). ORR was 79% (95% confidence interval (CI): 58-93); best responses were complete response in 3 (13%) patients, partial response in 16 (67%), stable disease in 3 (13%), progressive disease in 1 (4%) and not evaluable in 1 (4%). Median DoR and PFS were 35 (95% CI: 22-not estimable (NE)) and 44 (95% CI: 35-NE) months, respectively; 6-year OS rate was 71% (95% CI: 50-91). Six patients remained on treatment. Treatment-related adverse events (TRAEs) were mainly grade 1/2; no patients permanently discontinued treatment due to TRAEs. Larotrectinib continues to demonstrate durable disease control, extended survival and a favourable long-term safety profile in patients with advanced TRK fusion DTC requiring systemic therapy.