title: Merkel cell (primary neuroendocrine) carcinoma of the skin with nodal metastasis showing rhabdomyosarcomatous differentiation.
abstract: BACKGROUND
  We describe a unique case of Merkel cell (primary neuroendocrine) carcinoma of the skin with a lymph node metastasis showing rhabdomyosarcomatous differentiation. Skeletal muscle differentiation has occasionally been described in primary small cell neuroendocrine carcinomas and considered a form of dual differentiation rather than a collision tumor. In the present case, capacity for divergent differentiation appeared late in the course of the tumor, which suggests a clonal origin for both components of the neoplasm.
  
  
  CONCLUSIONS
  The coexistence of neural and rhabdomyoblastic types of differentiation, best epitomized by the Triton tumor, has been construed as the product of dual differentiation of cells originated from neural crest-derived ectomesenchyme. Since Merkel cells seem to originate from a pluripotential primitive keratinocyte and not from the neural crest, rhabdomyoblastic differentiation in a metastasis of primary neuroendocrine carcinoma of the skin probably reflects the close proximity between the programs of neural and skeletal muscle differentiation, which would have been sequentially activated in the case we are reporting.
authors.affiliation: Department of Pathology, Hospital Universitari Germans Trias i Pujol, Badalona, Spain. mtferfig@ns.hugtip.scs.es
authors.forename: María-Teresa
authors.initials: MT
authors.lastname: Fernández-Figueras
authors.forename: Lluís
authors.initials: L
authors.lastname: Puig
authors.forename: Montserrat
authors.initials: M
authors.lastname: Gilaberte
authors.forename: María del Carmen
authors.initials: Mdel C
authors.lastname: Gómez-Plaza
authors.forename: Jordi
authors.initials: J
authors.lastname: Rex
authors.forename: Carlos
authors.initials: C
authors.lastname: Ferrándiz
authors.forename: Aurelio
authors.initials: A
authors.lastname: Ariza
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D014408:Biomarkers, Tumor / Q000032:analysis; D015266:Carcinoma, Merkel Cell / Q000737:chemistry / Q000556:secondary* / Q000601:surgery; D002471:Cell Transformation, Neoplastic / Q000378:metabolism / Q000473:pathology*; D002999:Clone Cells; D018572:Disease-Free Survival; D005260:Female; D006801:Humans; D007124:Immunoenzyme Techniques; D008198:Lymph Nodes / Q000473:pathology; D008207:Lymphatic Metastasis; D012208:Rhabdomyosarcoma / Q000737:chemistry / Q000556:secondary* / Q000601:surgery; D012878:Skin Neoplasms / Q000737:chemistry / Q000473:pathology* / Q000601:surgery; D016896:Treatment Outcome
chemical_list: D014408:Biomarkers, Tumor