Anaplastic lymphoma kinase-positive diffuse large B-cell lymphoma with a complex karyotype and cryptic 3' ALK gene insertion to chromosome 4 q22-24

Anaplastic lymphoma kinase (ALK)-positive diffuse large B-cell lymphoma (DLBCL) is a rare tumor that is frequently associated with t(2;17)(p23;q23), a translocation fusing the ALK gene at 2p23 to the clathrin heavy chain gene (CLTC) at 17q23. Here, we report a unique case of ALK-positive DLBCL with plasmablastic morphology and focal cytoplasmic granular ALK stain in an HIV-negative 33-year-old man. By conventional karyotyping, the lymphoma cells were near-tetraploid and included 4 structurally normal copies each of chromosomes 2 and 17. Fluorescence in situ hybridization revealed an apparently normal, intact ALK gene on each of the 4 chromosome 2 homologs plus a cytogenetically cryptic ALK gene insertion into 2 of the 4 chromosome 4 homologs at band 4q22-24. The lymphoma cells expressed CD138, lambda light chain, focal and weak CD30, and exhibited aberrant T-cell antigens, including perforin. This case indicates that ALK-positive DLBCL is more heterogeneous at the cytogenetic/molecular level than previously recognized.