The LCH-IV is an international, multicenter, prospective clinical study for pediatric Langerhans Cell Histiocytosis LCH (age < 18 years). LCH is a rare disease of the immune system that may affect any age group. It can affect many different organs, including the skeleton, skin, lymph nodes, liver, lungs, spleen, hematopoiesis, or central nervous system (CNS). There are two widely recognized disease extent categories: single-system LCH (involvement of a single organ or system) and multisystem LCH (involvement of 2 or more organ systems). Patients with SS-LCH of the skeleton, skin, or the...