[CD20-positive T cell lymphoma: clinicopathological features of five cases].

Objective: To investigate the clinicopathological characteristics of the T cell lymphomas with CD20 expression, and to better understand this rare entity. Methods: Two-hundred cases of T-cell lymphoma diagnosed in the Department of Pathology of the Affiliated Hospital of Qingdao University from November 2016 to February 2020 were examined, and 5 cases of CD20-positive T-cell lymphomas were identified and included. Combined with clinical data and review of the literature, the clinicopathological characteristics of the disease were analyzed. Results: The five patients were all male, and had an average age of 56 years (range, 47 to 64 years). There were 2 cases of monomorphic epitheliotropic intestinal T-cell lymphoma, 2 cases of mycosis fungoides (1 case was plaque stage and the other was tumor stage) and 1 case of indolent T-cell lymphoproliferative disorder of the gastrointestinal tract. Immunohistochemistry showed that all 5 cases expressed multiple T cell markers (CD3/CD4/CD5/CD7/CD8) and only one of B cell markers (CD20). Three of the 5 cases were negative for CD20 at the first diagnosis, while CD20 was diffusely positive on the second biopsy from the recurrence or progression of the disease, without expression of CD79a or PAX5. Epstein-Barr encoding region (EBER) in situ hybridization was negative in all 5 cases. T-cell receptor gene analysis showed monoclonal rearrangement of β or/and δ chains;Ig rearrangements were all polyclonal. None of the five patients were treated with rituximab, and 4 patients survived with disease and 1 patient survived without disease at the end of follow-up. Among them, the patient with mycosis fungoides at the cancerous stage has progressed rapidly and had poor quality of life. Conclusions: CD20-positive T-cell lymphoma is extremely rare. Its prognosis is closely related to the type of T-cell lymphoma, clinical stage and initial therapeutic effect. However, the expression of CD20 indicates the recurrence or progression of the disease, and the prognosis is relatively poor. When CD3 expression is absent in T-cell lymphoma, it is easy to be misdiagnosed as B-cell lymphoma. The combination of multiple immunohistochemical antibodies and molecular detection can improve the accuracy of diagnosis.