Table 1.

NTRK1-3 Testing Methodologies

Reverse transcriptase-polymerase chain reaction (RT-PCR)	▪ Variable sensitivity ▪ High specificity	▪ Fusion detection requires specific primers targeting suspected genes and exons ▪ Hindered by RNA degradation
RNA based NGS alone	▪ Ability to access for unknown fusion partners, including other oncogenic alterations as well as splice variants	▪ Hindered by RNA degradation
DNA-based NGS alone	▪ Access for point mutations, fusions, and copy number changes ▪ Limited sensitivity to detect NTRK3 fusions	▪ Reliant on decent tumor purity
Dual DNA/RNA based NGS	▪ Superior analysis while likely being the most expensive methodology	▪ Reliant on decent tumor purity
Fluorescent in situ hybridization (FISH)	▪ Comparable turn-around time (approximately 1–3 days) compared to IHC ▪ Designed to detect specific breakpoints	▪ Best utilized when there is high suspicion of ETV6-NTRK3 fusions
Pan-TRK IHC	▪ Ability to screen for NTRK1-3 fusions while remaining cost effective	▪ Limited specificity ▪ Detects physiologic wild-type TRK expression