Hemophagocytic lymphohistiocytosis: A rare, cancer-like disorder in which both histiocytes and lymphocytes start to proliferate and attack body tissues or organs. It can be an inherited condition, or it can occur as a result of immunosuppression (as in organ transplants) or infection. Most patients are young children. Treatment is by chemotherapy, and in some cases bone-marrow transplantation.
See also histiocytosis.