Anaplastic lymphoma kinase-positive diffuse large B cell lymphoma: immunohistochemical and FISH analysis of a rare tumor with unusual clinical presentation

Abstract

Anaplastic lymphoma kinase-positive diffuse large B cell lymphoma represents a distinct subtype of diffuse large B cell lymphoma with a characteristic morphology, a distinct immunophenotypic profile, and recurrent cytogenetic/molecular genetic abnormalities. We report a case of anaplastic lymphoma diagnosed in the bone marrow trephine of a 24-year-old male. Histologically, the tumor cells exhibited plasmablastic morphology with expression of CD45, CD138, EMA, MUM1, and kappa immunoglobulin light chain, but negative for CD20, CD30, CD79a, PAX-5, CD10, and lambda light chain. In addition, the neoplastic cells showed positive immunoreactivity for anaplastic lymphoma kinase (ALK) with exclusive cytoplasmic granular staining pattern. Furthermore, interphase fluorescence in situ hybridization analysis, revealed ALK gene rearrangement in the lymphoid cells. The diagnosis of this rare entity in unusual extranodal sites such as the bone marrow is challenging, and it is based on detailed morphological and immunohistochemical analysis. Fluorescence in situ hybridization provides also a helpful tool in order to establish the diagnosis.