The use of fluorescent in situ hybridization for detection of the t(2;5)(p23;q35) translocation in anaplastic large-cell lymphoma

Background: Anaplastic large-cell lymphoma (ALCL) is a recently recognized, distinctive type of non-Hodgkin's lymphoma characterized by anaplastic large-cell cytology and expression of a member of the TNF-receptor family CD30. A characteristic chromosomal translocation has been identified in ALCL of Tor null-cell lineage which juxtaposes a novel tyrosine kinase (anaplastic lymphoma kinase, ALK) located at 2p23 with the nucleophosmin gene (NPM) at 5q35. A chimeric mRNA transcript is produced, and the translocation results in constitutive expression of a truncated form of the ALK protein, p80. There is controversy concerning whether or not the translocation occurs in Hodgkin's disease. The aim of this study was to develop a methodology for fluorescent in situ hybridization (FISH) to detect the t(2;5)(p23;q35), and to compare the results with conventional cytogenetics, reverse-transcriptase PCR and immunostaining for the p80 protein. Patients and methods: Twenty-five cases of malignant lymphoma (II ALCL and 14 HD) were studied. Immunohistochemistry was performed to confirm the diagnosis and for analysis of p80 expression. Conventional cytogenetics were analyzed on C-banded metaphase spreads. FISH was performed using whole chromosome paints for chromosomes 2 and 5 on metaphase spreads and YAC probes for interphase nuclei. Reverse-transcriptase PCR using primers for ALK and NPM was used to amplify the translocation breakpoint in extracted mRNA. Results: Among 11 cases of ALCL examined by FISH, the translocation was detected in 4. Two of these cases also had RT-PCR and p80 staining performed, with positive results. Among 7 cases where the t(2;5) was not detected by FISH, 3 cases were examined by RT-PCR with negative results and 4 cases by p80 staining, also negative. The RT-PCR was negative in all 14 cases of Hodgkin's disease, 4 of which were also examined by FISH and found to be negative. Conclusion: Fluorescent in sib hybridization is a useful method for detection of the t(2;5)(p23;q35) in anaplastic large-cell lymphoma. The results concur with those of RT-PCR for the chimeric transcript and immunostaining for the p80 protein. The frequency with which the translocation was found was 36% in this small series, and no evidence of the translocation was found in cases of Hodgkin's disease.