[Bone and soft tissue Langerhans cell histiocytosis with multinucleated giant cells and BRAF V600E mutation]

Langerhans cell histiocytosis (LCH) is a heterogeneous disease characterized by proliferation of Langerhans cells and BRAF mutation in almost half of the cases. Bone involvement is common but large soft tissue disease is uncommon. We report a pediatric patient with a large tumor mass involving the left iliac bone and the adjacent soft tissue. The computed tomography scan showed an osteolytic lesion with soft tissue extension. Surgical curettage of the lesion was performed and the final histopathologic diagnosis was LCH with CD1a immunoreactivity in tumor cells. The molecular analysis revealed a BRAF V600E mutation. We discuss the histopathological and immunohistochemical differential diagnosis with histiocytosis other than LCH.