Single-Institution Experience of Larotrectinib Therapy for Patients With Fusion-Positive Thyroid Carcinoma.

Context: The real world efficacy and tolerabiltiy of NTRK inhibitor larotrectinib has not yet been reported in the literature although trial data has shown promising results.

Objective: We report a retrospective analysis of patients with thyroid cancer harboring fusions who underwent treatment with larotrectinib.

Methods: A single-institution, retrospective case series of patients with fusion-positive thyroid cancers treated with neurotrophic tyrosine receptor kinase ( inhibitors from January 1, 2007, to January 1, 2023, was performed. This study was conducted at a single academic tertiary referral center. Patients with confirmed -fusion thyroid cancer who received larotrectinib were included. Larotrectinib was administered in accordance with clinical judgment from oncology providers. The primary end point was progression-free survival (PFS).

Results: Eight patients with fusion-positive thyroid cancer treated with larotrectinib were identified: 4 with papillary thyroid cancer (PTC) (50%), 3 with poorly differentiated thyroid cancer (PDTC) (38%), and 1 with anaplastic thyroid cancer (ATC) (12%). The median PFS (mPFS) for all patients was 24.7 months (95% CI, 11.3-38.1). mPFS in PTC was higher than PDTC (34.6 months [24.7-48.7 months] vs 17.5 [7.1-21.1 months]; = .017). The median overall survival (OS) was 43.8 months (29.8-56.8 months) overall. The single patient with ATC had a PFS and OS of 23 months. Two patients remained on treatment/alive at data cutoff, with a duration of response of 33.5 months and a median follow-up of 52 months. Patients achieved 1 complete response (12%), 6 partial responses (75%), and 1 stable disease (12%).

Conclusion: In this single-institution cohort of patients with fusion-positive thyroid cancer, inhibition led to an mPFS of 25 months, with survival surpassing historic benchmarks for ATC and PDTC.