NTRK1 and neoplasm: Fluorescence in situ hybridization (FISH) was performed on 3 μm FFPE sections of tumour tissue using break apart probes for NTRK1, NTRK2, and NTRK3 (Z-2167, Z-2205, Z-2206; ZytoVision GmbH, Bremerhaven, Germany), each composed of a green-labelled probe for the 5′ part of NTRK, and an orange-labelled probe marking the 3′ tyrosine kinase domain.