NTRK1 and melanoma: There are three Xiphophorus orthologs of the EGFR gene: egfra, which encodes a tyrosine kinase receptor; egfrb, which is a proto-oncogene form termed INV-Xmrk; and ONC-Xmrk, a duplicated version of INV-Xmrk, which is highly expressed in melanoma where it is responsible for inducing oncogenic transformation [23,24,25,26,27].