ALK-positive large B-cell lymphoma (ALK  + LBCL) with aberrant CD3 expression

We report an unusual case of ALK1 + LBCL in a 58-year-old man with partial expression of CD3 without other T cell antigen expression. The tissue was evaluated with flow cytometry, immunohistochemistry, fluorescent in situ hybridization, and gene rearrangement studies. Gene rearrangement studies forIGH andTCR gamma were performed. Flow cytometry did not demonstrate any abnormal lymphoid populations. Tissue sectioning shows a malignant plasmacytic large cell neoplasm which expresses CD45 but is negative for CD20, CD79a, and PAX5. Plasmacytic markers CD138 and MUM1 are positive with kappa light chain restriction. Strong granular cytoplasmic expression of ALK is present. FISH showing disrupted ALK supports the diagnosis whileMYC,BCL6, andBCL2 are intact. Gene rearrangement studies show coexistingIGH andTCR gamma clones; however, theTCR peak was present within a polyclonal background suggesting the disputed cells are likely only a subset of the T cell population. ALK  + LBCL can present with an ambiguous immunophenotype, which warrants the use of multiple B cell, T cell, and plasmacytic antibodies. CD3 expression in this entity is rare and of uncertain clinical significance, but warrants further study.
Source: Journal of Hematopathology - Category: Pathology Source Type: research