CD30-positive diffuse large B-cell lymphoma with microvillous features: so-called microvillous lymphoma

A case of CD30-positive microvillous lymphoma (MVL) in an 87-year-old man who was encountered generalised lymphadenopathy is presented. Histopathologically, the tumour showed a morphological mimic of anaplastic large cell lymphoma (ALCL) with sinusoidal growth pattern. Immunohistochemically (IHC), the tumour cells were CD30(+), CD20(+), CD45(+), BCL-2(+), BCL-6(+), MUM1(+), Ki-67(+), CD45RO(-), CD3(-), CD10(-), CD15(-), CD56(-), EMA(-), TIA-1(-) and ALK(-). Flow cytometry confirmed the IHC. In situ hybridisation for Epstein-Barr virus RNA was negative. Electron microscopically, the tumour cells were similar to large transformed lymphocytes and had circumferentially profuse microvillous projections resembling those of epithelial mesothelioma cells. In conclusion, CD30-positive MVLs are indistinguishable from ALCLs that have ultrastructural microvillous projections by morphology alone. However, the lack of EMA, TIA-1 and ALK expression in this MVL case facilitated a definite distinction from ALCLs. The results of a panel of three markers (CD10(-), Bcl-6(+) and MUM1(+)) suggested that the present case of CD30-positive MVLs has an activated non-germinal centre B-cell origin.