Langerhans Cell Histiocytosis (LCH) is a type of cancer that can damage tissue or cause lesions to form in one or more places in the body. Langerhans cell histiocytosis (LCH) is a cancer that begins in LCH cells (a type of dendritic cell which fights infection). Sometimes there are mutations (changes) in LCH cells as they form. These include mutations of the BRAF gene. These changes may make the LCH cells grow and multiply quickly. This causes LCH cells to build up in certain parts of the body, where they can damage tissue or form lesions. For most patients with LCH, standard-of-care vinblastine/prednisone are used as front-line therapy while cytarabine therapy has been used as therapy for patients who develop recurrence. No alternate treatment strategy has been developed for frontline therapy in LCH. The purpose of this research study is to compare previously used vinblastine/prednisone to single therapy with cytarabine for LCH. We will evaluate the utility of an imaging study called a positron emission tomography (PET) scan to more accurately assess areas of LCH involvement not otherwise seen in other imaging studies as well as response to therapy. We also want to identify if genetic and other biomarkers (special proteins in patient's blood and in patient's cancer) relate to the response of patients LCH to study treatment.