Unclassifiable B-cell lymphoma occurring after necrotizing pneumonia.

We report a case of CD20+ grey zone lymphoma (GZL) with Reed Sternberg cells as an unexpected pathological diagnosis of a destroyed right lower lobe after necrotizing pneumonia. These GZLs show overlapping features of classical Hodgkin's lymphoma and diffuse large B-cell lymphoma. GZLs are a rare specific entity of lymphomas, and the aetiology is unknown. The diagnosis is confirmed by pathological, immunohistochemical and molecular analyses. The optimal treatment is unknown. The prognosis of these patients is poor.