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AIDS-associated B-cell non-Hodgkin's lymphoma masquerading as a cutaneous T-cell neoplasm: an aberrant immunophenotype requiring comprehensive analysis for lineage resolution.

An increased prevalence of intermediate- and high-grade B-cell non-Hodgkin's lymphoma (NHL) is a major manifestation of the disease spectrum associated with human immunodeficiency virus (HIV) infection. Rarely, lymphoproliferations are of T-cell, null cell, or mixed-lineage phenotypes. We describe an unusual B-cell NHL that presented as a left alar ulcer in a man with acquired immunodeficiency syndrome (AIDS) and rectal carcinoma. Biopsy of the lesion and a draining cervical lymph node showed atypical dermal lymphoid infiltration with effacement of nodal architecture and involvement of adjacent skeletal muscle by a diffuse infiltrate of large and small lymphocytes. On paraffin section immunochemistry, the large lymphoid cells expressed CD45 and CD45RO, but not CD43 or CD20. The small background cells were positive for CD3, CD43, and CD45RO. These overall results were consistent with a diagnosis of a T-cell process. Gene rearrangement studies, however, demonstrated a clonal B-cell population indicative of B-cell NHL. The clinical course was marked by rapid shrinkage of tumor with chemotherapy followed by profound wasting and death. Anomalous coexpression or lack of expression of T- and B-cell markers may be seen in AIDS-related NHL. Reliance on paraffin section immunohistology may provide misleading information, and caution is recommended in assigning a specific lineage to such lymphoproliferations without additional immunologic or genotypic analyses. Whether our case represents a distinct clinicopathologic entity or is simply a peculiar manifestation of HIV-related B-cell NHL remains uncertain.