RT-PCR analysis of CLTC-ALK and ALK extracellular domain transcripts. (A) Cases 1 and 5 (lanes 1-2) and the NIH3T3 cell line transfected with CLTC-ALK cDNA, used as positive control (lane 5), show the expected 270-bp CLTC-ALK RT-PCR product (M indicates size marker). No band could be amplified from the Rh30 (lane 3), NIH3T3 cell line transfected with ALK-EC cDNA (lane 4), SU-DHL1 (lane 6), and COST (lane 7) cell lines, used as negative controls. (B) Transcripts encoding the extracellular portion of ALK also were present in the cases expressing CLTC-ALK transcripts (lanes 1-2), as in the Rh30 (lane 3) cell line and in the NIH3T3 cell line transfected with ALK-EC cDNA (lane 4), used as positive controls. As expected, no signal was present in either of the t(2;5)-positive SU-DHL1 (lane 6) and COST (lane 7) cell lines, nor in the NIH3T3 cell line transfected with CLTC-ALK cDNA (lane 5).