The Langerhans' cell histiocytoses (LCH) are a group of related entities which share a common pathology. The Langerhans' cell histiocytoses include eosinophilic granuloma, Hand-Schuller-Christian disease and Letterer-Siwe disease. These entities are all characterized by a proliferation of Langerhans' cells and are best thought of as monostotic, polyostotic or disseminated forms of the same disease. The malignant potential of this group of diseases is uncertain and treatment should be discussed with a medical oncology member of the Lymphoma Tumour Group at one of the BCCA Centers.

True malignant histiocytosis is a rare disease and is best considered a variant form of malignant lymphoma. Hemophagocytosis by cytologically malignant-appearing cells is typically seen in histologic sections and diagnosis requires careful morphologic and phenotypic assessment. The behaviour is usually similar to that of a large cell lymphoma and treatment should be given as for large cell lymphoma taking into account the stage of the disease and the age of the patient.