The CD246 antigen, or ALK (Anaplastic Lymphoma Kinase; neural tyrosine kinase) is a 200 kDa transmembrane molecule expressed only in neural tissues (weakly) and by the rhabdomyosarcoma Rh30 cell line. The alk gene is on chromosome 2. Upon translocation between chromosome 2 and chromosome 5 [t(2;5)], the alk gene fuses with the npm gene. NPM, also known as nucleophosmin or B23, is an ubiquitous nucleolar phosphoprotein involved in the transport of pre-ribosomal components between the nucleolus and the cytoplasm. The chimeric product resulting from t(2;5) translocation is a protein of 80 kDa with the N-terminal portion of NPM linked to the complete intracellular portion of ALK. Karpas 299 and SU-DHL-1 lymphoid cell lines strongly express NPM-ALK.