Anaplastic lymphoma kinase (ALK) is not expressed in Hodgkin's disease: Results with ALK-11 antibody in 327 untreated patients

The t(2;5)(p23;q35) or other rare chromosomal abnormalities involving 2p23 upregulate the ALK gene, which is not expressed in normal lymphocytes. Thus , detection of ALK protein is presumptive evidence of these 2p23 abnormalit ies. The t(2;5) and ALK immunoreactivity are common in anaplastic large cel l lymphoma of T/null-cell lineage. However, a small subset of cases of Hodg kin's disease (HD) have been reported to either carry the t(2;5) or express ALK. In this study, we have immunohistochemically evaluated 327 cases of H D with the ALK-11 antibody. ALK-11 is a well characterized polyclonal antib ody raised against an intracellular portion of the ALK protein. We detected ALK-11 immunoreactivity in 8 (2.4%) cases of HD. We further studied these positive cases with ALK-1 monoclonal antibody, which reacts with an intrace llular portion of ALK, similar to ALK-11. All 8 ALK-11 positive cases were negative for ALK-1. These results indicate that rare cases of HD may react with ALK-11 antibody, similar to previous reports by others using different polyclonal anti-ALK antibodies, However, the absence of ALK-1 expression i n these HD cases suggests that ALK protein is not truly present and that po lyclonal anti-ALK antibodies may rarely yield non-specific cross reactivity . These results further support the use of anti-ALK antibodies in the diffe rential diagnosis of IID from ALCL.