T-cell large granular lymphocytic leukemia (T-cell LGLL) is a rare disorder characterized by the monoclonal expansion of CD3-positive cytotoxic T cells. Cell morphology and immunophenotyping are the main tools for diagnosis. Typical phenotypic findings include the expression of markers CD3+, CD5+dim, CD8+, CD16+, CD57+, and T-cell receptor (TCR) αβ (+). However, a few cases may present with the CD3+/CD4+ phenotype or the double expression of CD4 and CD8. Similarly, in 20% of cases, TCRγ/δ is positive. In this study, we aimed to describe a rare, unusual case of T-cell LGLL that exhibited expression of the B-cell antigen, CD20. Additionally, we performed a literature review to compare the clinical characteristics of our patient to those of other patients with CD20-positive T-cell LGLL and to seek new therapeutic possibilities.

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