ALK-positive extramedullary plasmacytoma with expression of the CLTC-ALK fusion transcript

Anaplastic lymphoma kinase (ALK)-positive non-Hodgkin lymphoma (NHL) was long thought to be a disease occurring uniquely in T or null-cell lymphomas. More recently, however, a small number of B-lineage lymphomas have been reported to express ALK fusion genes. These tumors often exhibit a plasmablastic morphology, a finding which prompted our interest in looking for ALK fusions in plasma cell neoplasms. We studied 46 cases of extramedullary plasmacytoma by immunostaining with anti-ALK antibody and fluorescence in situ hybridization (FISH) analysis using an ALK break-apart probe and found one case to be ALK protein-positive and demonstrated the disruption of the ALK gene in this case. Immunohistochemistry showed that the tumor cells were strongly positive for CD138, VS38c, and epithelial membrane antigen, but lacked expression of CD20, CD79a, CD45, and CD30. Both RT-PCR and genomic DNA-PCR confirmed the CLTC-ALK fusion. This finding expands the lists of the ALK-positive tumors, and ALK-positive extramedullary plasmacytoma may benefit from the treatment of ALK inhibitor in the future.