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A rare case of intravascular large T-cell lymphoma with an unusual T helper phenotype.

Although most cases of intravascular large cell lymphoma exhibit a B-cell phenotype, less than 50 cases in the literature describe a T-cell or natural killer cell phenotype and, of these, the majority are CD3+, CD4-, CD5-, CD30-, CD56+, TIA-1+, and EBER+. We present a case of a rare intravascular large T-cell lymphoma in a 59-year-old man with an unusual CD3+, CD4+, CD5-, CD30+, CD56-, TIA-1-negative and EBER-negative phenotype. This T helper or CD30 phenotype is particularly uncommon. To our knowledge, it has only been described once before and never in the absence of the cytotoxic marker TIA-1. This case exemplifies the particular diagnostic challenges raised by intravascular large cell lymphomas generally and should encourage the use of endothelial immunohistochemical staining in questionable cases. While evaluating skin punch biopsies, it is critical to keep this rare entity on the differential diagnosis along with the relatively more common intravascular large B-cell lymphoma and epithelial malignancies. Additionally, our understanding of intravascular large natural killer/T-cell lymphoma as a heterogeneous phenotypic entity continues to evolve. This case demonstrates that the degree of this phenotypic heterogeneity may be even greater than previously thought.