Adult T cell leukemia/lymphoma complicated by proliferation of large B cells: a diagnostic dilemma

Peripheral T cell lymphomas are clinically and pathologically complex and generally associated with overall poor prognosis and aggressive clinical course. In recent years, there is a greater recognition of abnormal B cell expansion as a component of T cell lymphomas especially those derived from follicular helper T cells. Most of these B cells are EBV positive and show a wide range of morphology which includes large mononuclear cells and Hodgkin-like cells. The number of the abnormal B cells can also vary. It is possible to misdiagnose this entity as a B cell lymphoma, Hodgkin lymphoma, composite lymphoma, or reactive lymphoid proliferation based on the number and morphology of the proliferating B cells. Herein, we report the case of an 82-year-old woman who presented with cervical lymphadenopathy, excision biopsy of which showed diffusely arranged atypical small- to medium-sized cells with irregular nuclei admixed with large number of immunoblast-like large cells. Immunophenotyping showed the small- to medium-sized cells to be CD20 negative, CD3 positive, and CD5 positive and showed downregulation of CD7. These cells were CD25 positive and showed a high MIB 1 labelling index. The large cells were CD20 positive and CD30 positive and showed EBV-encoded small nuclear RNA (EBER) positivity. Serum HTLV-1 estimation was positive. Molecular studies showed TCR gene rearrangement and a polyclonal population of B cells. Based on morphology, immunoprofile, and molecular studies, a diagnosis of adult T cell leukemia/lymphoma complicated by proliferation of large B cells was given. The presence of large B cell proliferation in adult T cell leukemia/lymphoma is an exceptionally rare phenomenon.