Nodal T-Cell Lymphoma Transdifferentiated from Mantle Cell Lymphoma with Epstein-Barr Virus Infection.

Introduction: We report a case of mantle cell lymphoma (MCL) with an apparent lineage switch to an EBV-positive T-cell lymphoma. Although lineage switch is a well-documented phenomenon in some hematolymphoid diseases, such as acute leukemias or histiocytic/dendritic cell neoplasms, lineage switch from mature B-cell to T-cell lymphoma is exceedingly rare.

Case Presentation: A 55-year-old man with an established history of MCL presented to our institution. Peripheral blood flow cytometry was consistent with MCL. Biopsy of a lumbar vertebral fracture site demonstrated MCL, EBV-associated, with large cells reminiscent of high-grade transformation (BCL1-positive). Two months later, a lymph node biopsy demonstrated an EBV-positive T-cell lymphoma without phenotypic evidence of B-cell lymphoma (BCL1-negative). Cytogenetic testing revealed CCND1::IGH fusion in all three specimens. IGH/IGK clonality testing revealed conserved monoclonal peaks in all three samples; TCR clonality testing revealed monoclonal peaks in the T-cell lymphoma, only. NGS-based molecular genetic studies revealed shared mutations between the three samples, consistent with a clonal relationship suggesting evolution from MCL to T-cell lymphoma.

Conclusions: This case demonstrates that lineage switch from mature B-cell to mature T-cell phenotype is possible in certain settings. Whether lineage switch in this case was potentiated by EBV infection is unclear. The loss of BCL1 expression in the T-cell lymphoma, despite conservation of the CCND1::IGH fusion, may be attributable to the downregulation of the IGH promoter as part of the shift from B-cell to T-cell phenotype.