label: ALK-Positive Histiocytosis
label_lc: alk-positive histiocytosis
description: A rare histiocytic neoplasm associated with ALK gene rearrangement leading to activation of signaling pathways. The neoplastic cells have a mature histiocytic phenotype, and usually have a foamy cytoplasm. It is characterized by frequent neurologic involvement and responds to ALK inhibition treatments.