Immunohistochemical (IHC) testing for NTRK (Neurotrophic Tyrosine Receptor Kinase 1/2/3) proteins aims to detect abnormal or excessive protein expression of TRKA, TRKB, or TRKC, which may indicate a gene fusion in the NTRK1, NTRK2, or NTRK3 genes. This test is a rapid and cost-effective initial screening tool for identifying patients who may have tumors containing NTRK fusions and are targeted by TRK inhibitor drugs (such as larotrectinib and entrectinib).