title: Merkel cells, normal and neoplastic: an update.
abstract: Merkel cells (MC) occur in the basal epidermal layer, hair follicles, and oral mucosa, as complexes with sensory axons. The axons transduce slowly adapting type I mechanoreception, and MC modulate their sensitivity. MC also determine and maintain the 3-dimensional epidermal structure. They have neuroendocrine granules, rigid spinous processes, and desmosomal junctions with each other and with keratinocytes. Rare MC are dermaWl. Current evidence supports a basal cell origin. Merkel cell carcinomas (MCC) occur mostly in sun-exposed skin in old age. Trabecular, intermediate, or small cell in pattern, MCC have neuroendocrine granules, intercellular junctions, rigid spinous processes, and a paranuclear collection of intermediate filaments staining for cytokeratin 20. Most MCC behave indolently, but those with the small cell pattern, and some with the intermediate pattern, are aggressive and rapidly fatal.
authors.affiliation: The New York Harbor Healthcare System and New York University School of Medicine, New York, New York 10010, USA. deepsidhu@optoline.net
authors.forename: Gurdip S
authors.initials: GS
authors.lastname: Sidhu
authors.forename: Pranil
authors.initials: P
authors.lastname: Chandra
authors.forename: Nicholas D
authors.initials: ND
authors.lastname: Cassai
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000032:analysis; D051927:CD24 Antigen; D015266:Carcinoma, Merkel Cell / Q000378:metabolism / Q000473:pathology / Q000648:ultrastructure*; D006801:Humans; D007150:Immunohistochemistry; D007381:Intermediate Filament Proteins / Q000032:analysis; D053554:Keratin-20; D008562:Membrane Glycoproteins / Q000032:analysis; D018862:Merkel Cells / Q000648:ultrastructure*; D008854:Microscopy, Electron; D018396:Mucin-1 / Q000032:analysis; D039842:Neural Cell Adhesion Molecule L1 / Q000032:analysis; D016900:Neurofilament Proteins / Q000032:analysis; D012867:Skin / Q000737:chemistry / Q000473:pathology / Q000648:ultrastructure; D012878:Skin Neoplasms / Q000378:metabolism / Q000473:pathology / Q000648:ultrastructure*
chemical_list: D015703:Antigens, CD; D051927:CD24 Antigen; C497889:CD24 protein, human; D007381:Intermediate Filament Proteins; C507499:KRT20 protein, human; D053554:Keratin-20; D008562:Membrane Glycoproteins; D018396:Mucin-1; D039842:Neural Cell Adhesion Molecule L1; D016900:Neurofilament Proteins