[Clinicopathological features of mature T/NK cell lymphoma with aberrant CD20 or CD79α expression].

To investigate the clinicopathological characteristics and prognosis of mature T/NK cell lymphomas with aberrant CD20 or CD79α expression. A retrospective analysis of 641 cases of mature T/NK cell lymphoma diagnosed from January 2014 to December 2020 was performed, and 14 cases of CD20-positive and one case of CD79α-positive mature T/NK-cell lymphoma were identified. Histological examination, immunohistochemical characterization, in situ hybridization for Epstein-Barr virus encoded early RNA (EBER), and PCR testing for immunoglobulin and T cell receptor (TCR) gene rearrangements were performed. Clinicopathological characteristics of these lymphomas were analyzed. There were 13 males and 2 females, with a median age of 56 years. There were 8 cases of peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS), 3 cases of extranodal NK/T-cell lymphoma, nasal type (ENKTCL), 2 cases of monomorphic epitheliotropic intestinal T-cell lymphoma (MEITL) and 2 cases of angioimmunoblastic T-cell lymphoma (AITL). Twelve cases were stage Ⅲ or Ⅳ lymphomas. The prognosis was overall poor. The histology, immunophenotype and TCR gene rearrangement were not significantly different from the corresponding types of lymphoma. Ki-67 proliferation index was over 70% in all cases. The expression of CD20 or CD79α was weak and heterogeneous. All 15 case of Ig gene rearrangement were polyclonal. Mature T/NK cell lymphoma with abnormal expression of CD20 or CD79α is rare, commonly found in advanced stage, and associated with poor prognosis. The expression of CD20 or CD79α in these cases is weaker than the corresponding mature T/NK cell lymphomas, while its proliferation index is higher. Histomorphology, extensive immunoprofiling and molecular detection are required for accurate diagnosis.