Histiocytosis--an introduction.

The Histiocytoses are a group of rare and puzzling multisystem disorders, currently regarded as non-malignant but often treated with 'cancer chemotherapy'. In this article, the origins of histiocytes and of the Histiocyte Society's classification of the Histiocytoses are described with suggested minor modifications to the classification. The current nomenclature for the 2 principal diseases, now named 'Langerhans cell histiocytosis' and 'Haemophagocytic Lymphohistiocytosis', is less confusing than the terms originally chosen. The article sets the scene for the succeeding papers, which focus on 'Langerhans cell histiocytosis'.