Clinical, pathological, and radiographic features of LCH with cutaneous toxicities of MAPK inhibitors. (A) Scaly scalp rash in a 2-year-old boy. (B) LCH with a rich inflammatory background including osteoclast-like giant cells, eosinophils, and neutrophils (hematoxylin and eosin). (C) Immunostain showing surface CD1a expression. (D) Mutant-specific BRAF-VE1 immunostain with dark granular cytoplasmic staining in the lesional histiocytes (immunostain 400 × ). (E) Granulomatous CNS-LCH: brain MRI sagittal T1W image lacking posterior pituitary bright spot. (F) Brain MRI in a patient with granulomatous CNS-LCH: axial contrast-enhanced T1W image showing extensive bilateral lesions in the choroid plexus. (G) ND-LCH: axial T2-weighted image showing extensive dentate nucleus and white matter cerebellar neurodegeneration. (H) Skin hyperkeratosis pilaris of the left arm in a patient treated with a BRAF inhibitor. (I) Lobular panniculitis of the right leg in a patient on a MEK inhibitor. (J) Cutaneous squamous cell carcinoma in a adult treated with a BRAF inhibitor.