Examples of Responses of BRAF V600E and MAP2K1 Mutant Adults with Erdheim-Chester Disease (ECD) to Molecularly Targeted Therapies. A) Positron emission tomography (PET) scan and brain MRI of a BRAF V600E-mutant ECD patient with skeletal and parenchymal brain lesions pre- and eight-weeks post-treatment with the BRAF inhibitor vemurafenib. B) PET scan of a MAP2K1 Q56P-mutant ECD patient with disease infiltration in facial sinuses, heart, and kidneys pre- and four-weeks post-treatment with the MEK 1/2 inhibitor cobimetinib.