Langerhans cell histiocytosis: A neoplastic disorder driven by Ras-ERK pathway mutations

Langerhans cell histiocytosis (LCH) is a disorder of myeloid neoplasia of dendritic cells that affects 1 in 200,000 children <15 years of age and even fewer adults. LCH presents with a spectrum of clinical manifestations. High-risk stratification is reserved for infiltration of blood, spleen, liver, and lungs. After decades of debate on the disease pathogenesis, a neoplastic mechanism is now favored on the basis of LCH cell clonality, rare cases of familial clustering, and recent evidence of mutations involving the Ras/Raf/MEK (mitogen-activated protein kinase kinase)/ERK (extracellular signal-regulated kinase) pathway in lesional biopsy specimens.