Six Cases of CD20-Positive Adult T-Cell Leukemia

Adult T-cell leukaemia/lymphoma (ATLL) is a neoplasm originating in mature CD4⁺ peripheral T cells. However, rare cases of CD20⁺ ATLL have been reported. Here, we describe six cases of CD20⁺ ATLL diagnosed in our department. The median age was 79 years (range, 54-90 years); two patients were men, and four were women. Elevated lactate dehydrogenase was observed in four cases. All cases were lymphoma type and positive for human T-lymphotropic virus-1 (HTLV-1). HTLV-1 proviral DNA was detected in four cases. The Ann Arbor stage was I, II, or IV in one patient each and III in three patients. The clinical course was poor in almost all cases. Tumour cells were large in all cases, and flow cytometry revealed CD20⁺ lymphoma cells in five of six cases. Immunohistochemistry revealed lymphoma cells positive for CD20, CD3, CD4, and CCR4 and negative for CD8, CD79a, and PAX5 in all cases. CD20 expression was lower than that in normal B cells. One case was initially misdiagnosed as diffuse large B-cell lymphoma. Thus, combined use of an antibody panel and molecular genetic studies is important to avoid misdiagnosing ATLL as B-cell lymphoma.