The TRK fused gene refers to a genetic alteration involving the neurotrophic tyrosine receptor kinase (NTRK) genes. These genes, when fused with other genes, can lead to the production of abnormal proteins that drive cancer cell growth. The primary genes involved in these fusions are NTRK1, NTRK2, and NTRK3. These fusions can occur in various types of cancers, including rare tumors and more common ones.