Case 5 -

Anaplastic Large Cell Lymphoma of T/null-cell Phenotype, Systemic Type (ALK-Positive), Monomorphic Variant D. Ashley Hill, M.D. Mihaela Onciu M.D.

Case History: A15-year-old boy presented with three-week fever, not responding to antibiotics, and isolated left inguinal lymphadenopathy. An excisional lymph node biopsy was performed. The excised inguinal lymph node measured 2.5 cm in greatest dimension. No additional disease was identified at staging work-up. Microscopic Findings: Within the enlarged lymph node the architecture was subtotally effaced by a lymphoid tumor with diffuse growth pattern and interfollicular distribution. At low magnification the tumor had a "starry-sky" appearance imparted by frequent "tingible-body" macrophages scattered throughout the infiltrate. The relatively monotonous tumor cells were predominantly large, with irregular nuclear outline and abundant pale amphophilic cytoplasm. Frequent mitotic figures were noted. Differential Diagnosis: Burkitt lymphoma Diffuse large B-cell lymphoma Peripheral T-cell lymphoma, unspecified Anaplastic large cell lymphoma, monomorphic variant. Immunophenotypic Findings (Immunohistochemistry): The tumor cells were strongly and diffusely positive for CD45, CD43, CD30, ALK, and EMA, weakly positive for CD3 and CD45RO, and negative for CD20. The latter stain highlighted the small residual normal follicles, and the interfollicular (paracortical) growth pattern of this neoplasm. Molecular/Cytogenetic Analysis: RT-PCR positive for the NPM-ALK fusion transcript. Conventional cytogenetic analysis: positive for the t(2;5)(p23;q35) translocation. Diagnosis: Anaplastic large cell lymphoma of T/null-cell phenotype, systemic type (ALK-positive), monomorphic variant.