ALK-positive diffuse large B-cell lymphoma of the duodenum: A case report and review of the literature.

Anaplastic lymphoma kinase (ALK)-positive diffuse large B-cell lymphoma (ALK DLBCL) is characterized by the presence of immunoblastic or plasmablastic cells with a strong ALK protein expression that is frequently associated with t(2;17)(p23;q23). The present study reports a case of ALK DLBCL in a 26-year-old male with a duodenal mass. Histologically, the neoplastic cells demonstrated prominent plasmablastic differentiation with abundant amphophilic cytoplasma and central nucleoli. Paraffin immunohistochemistry revealed: an exclusively cytoplasmic granular expression of ALK; CD138, immunoglobulin A (IgA) and CD79α positivity; and focal expression of multiple myeloma oncogene 1 (Mum-1), CD30 and epithelial membrane antigen (EMA). However, the immunohistochemical staining was negative for CD3, CD38 and CD20. Fluorescence hybridization (FISH) analysis using an ALK break-apart probe revealed the presence of ALK gene rearrangements in the patient. To the best of our knowledge, the current case represents the first example of primary extranodal ALK DLBCL presenting as a duodenal mass.