 Erdheim-Chester Diseases ECD is a very rare non-Langerhans cell histiocytosis of unknown origin and pathogenesis. It has been reported mainly in adult males over the age of 40 years, although cases have been reported in females as well. Children are rarely affected. Mutation of the BRAF gene, specifically BRAFV600E, has been recently identified in 50 of Erdheim Chester lesions in a French cohort. This somatic mutation is believed to be the driver mutation in positive cases. The clinical characteristics of ECD range from asymptomatic to multisystemic involvement; longitudinal progression and natural history are becoming better understood. ECD commonly affects the bones, kidneys, retroperitoneal space, skin and brain. If untreated, the disease progresses rapidly, causing fatal outcomes due to severe lung disease, chronic renal failure, cardiomyopathy and other complications. The diagnosis of ECD relies upon imaging studies and specific pathologic findings in biopsies of affected organs, i.e., fibrosis and infiltration of tissues with foamy histiocytes, lymphocytes, and plasma cells. Immunohistochemistry reveals cells positive for CD68 and CD163 and negative for CD1a, with 20 positivity to S-100. There is no standard treatment for ECD, although chemotherapy, radiation, stem cell transplantion, alpha-interferon, anakinra, imatinib and sirolimus have been proposed. The recent discovery of the BRAFV600E mutation in several ECD patients has opened a new area for treatment options. Vemurafenib, an FDA approved BRAF inhibitor for the treatment of patients with metastatic or unresectable melanoma with the V600E mutation, binds to this form of mutated BRAF causing protein inactivation. The use of vemurafenib in patients with ECD has been reported in 3 patients who experienced remission of the disease, and is currently being studied in the U.S. and Europe as monotherapy. Tumordisease resistance to vemurafenib has occurred in melanoma and other cancers, although it has not been reported in patients with ECD. In this protocol, we propose to clinically evaluate ECD patients with the BRAFV600E mutation and administer combination therapy with dabrafenib, a BRAFV600E inhibitor, and trametinib, an inhibitor of MEK, downstream of BRAF. Screening for possible contraindications will be made prior to the administration of the first dose. With this trial, we will determine the safety, tolerability, and efficacy of dabrafenib and trametinib in patients with ECD who harbor the BRAFV600E mutation. Dabrafenib 150mg will be given twice daily p.o.; trametinib 2mg will be given once daily p.o. Patients will be seen 1 week, 1 month, 2 months, 4 months, and 6 months, 8 months, 10 months and 12 months to complete a oneyear trial. 