Malignant histiocytosis‐like B‐cell lymphoma, a distinct pathologic variant of intravascular lymphomatosis: a report of five cases and review of the literature

Malignant histiocytosis (MH)‐like B‐cell lymphoma (BCL) is a neoplastic proliferation of large B cells clinically characterized by fever, hepatosplenomegaly, haemophagocytosis and abnormal laboratory data, without lymphadenopathy or skin lesions. Interestingly, most cases have been reported in Asian patients, and it is unclear whether MH‐like BCL is biologically distinct from conventional large B‐cell lymphomas. We report five Japanese patients with MH‐like BCL. Biopsied specimens of bone marrow, liver and/or spleen showed infiltration of neoplastic B cells accompanied by haemophagocytosing histiocytes. Lymphoma cells were positive for CD19, CD20 and HLA‐DR surface antigens, and negative for CD5 and CD10. In four cases elevated serum levels of interleukin (IL)‐6 and the soluble IL‐2 receptor isoform were noted, but not IL‐1β, IL‐2 or tumour necrosis factor‐α. Autopsies of two cases were pathologically diagnosed as intravascular lymphomatosis (IVL). Based on these observations, the current and nine previous cases reported as MH‐like BCL in Japan were re‐evaluated. They appear to form a peculiar variant of IVL, characterized by bone marrow involvement at presentation, haemophagocytic syndrome, and a rapidly aggressive clinical course, but rarely neurological complications or skin lesions. This variant may merit separate consideration because of the problems posed in the initial diagnosis and therapeutic approaches.