(A) RT-PCR analysis of TPM3-ALK RNA in 3 cases of ALCL showing ALK-staining restricted to the cytoplasm. RNA obtained from the SU-DHL-1 cell line was used as negative control (T−). RT-PCR was performed using two rounds of PCR. The first round involved C-TPM1 and ALK-1 primers, and the second was a nested amplification using C-TPM3 and ALK-2 primers. PCR products were electrophoresed on 2% agarose gel and visualized with ethidium bromide staining. Two of these three cases of ALCL (cases no. 1 and 3) show a band of 307 bp, indicating the presence of hybrid TPM3-ALK RNA. M, size marker. (B) Nucleotide sequence of hybrid TPM3-ALK transcripts detected by nested RT-PCR using C-TPM3 and ALK2 primers. Nucleotides are numbered from the deoxyadenosine residue of the TPM3 initiator ATG codon.