RT-PCR with primers detecting ALK mRNA corresponding to the tyrosine kinase domain of the ALK receptor. Total RNAs extracted from the t(2; 5)-bearing SU-DHL1 cell line (lane C+) and a t(2; 5)-positive case of ALCL (lane 1) show the expected band of 366 bp. Note that the two cases (cases 1 and 6) under study (lanes 2 and 3), which are negative for NPM-ALK transcripts, also show a band of 366 bp. RNA from the CEM T-cell line yielded no product (C−). NoT, no template cDNA, MW, molecular-weight markers.