Langerhans cell histiocytosis (LANG-er-hanz sel HIS-tee-oh-sy-TOH-sis)
A group of rare disorders in which too many Langerhans cells (a type of white blood cell) grow in certain tissues and organs including the bones, skin, and lungs, and damage them. Langerhans cell histiocytosis may also affect the pituitary gland (which makes hormones that control other glands and many body functions, especially growth). Langerhans cell histiocytosis is most common in children and young adults. Also called LCH.