NTRK1 and melanoma: Studies in human melanoma cell lines and the Xiphophorus cross-derived melanoma cell line (PSM-1) [8] using chimeric receptors combining the human epidermal growth factor receptor (HER) with Xmrk (HER-mrk) have shown that Xmrk displays constitutive autophosphorylation and is a functional receptor tyrosine kinase with activity in malignant melanoma [9].