ALK-staining patterns in anaplastic large cell lymphoma.

The cellular localization of the fusion protein is influenced by the ALK partner. The majority of anaplastic large cell lymphomas (70%-80%) are associated with the (2;5)(p23;q35) translocation and express NPM-ALK fusion protein. In such cases ALK staining is cytoplasmic, nuclear, and nucleolar associated. Approximately 10% to 20% (unpublished data) of cases carry the (1;2)(q25;p23) translocation and express the TPM3-ALK fusion protein, which is restricted to the cytoplasm (diffuse staining). In clear contrast, the 2 cases in the present study show intracytoplasmic finely granular clusters of staining, a pattern that differs clearly from those previously described (the 2 insets show single cells positive for CLTCL-ALK, at high power).