title: Combined Merkel cell carcinoma and atypical fibroxanthoma.
abstract: BACKGROUND
  Although there are reports of squamous cell carcinoma arising within and adjacent to Merkel cell carcinoma, and one report of an atypical fibroxanthoma-like tumor arising in an irradiated recurrent Merkel cell carcinoma, there have previously been no reports of an immunohistochemically verified atypical fibroxanthoma occurring in conjunction with a Merkel cell carcinoma.
  
  
  OBJECTIVE
  We report on a neoplasm with distinct features of both Merkel cell carcinoma and atypical fibroxanthoma.
  
  
  METHODS
  Histologic and immunohistochemical evaluations were performed.
  
  
  RESULTS
  Our results verify the finding of a combined Merkel cell carcinoma and atypical fibroxanthoma.
  
  
  CONCLUSIONS
  This case is an interesting and unusual combination of tumors. The origin of the Merkel cell carcinoma is revisited. Debated origins include neuroendocrine, epithelial, and pleuripotent stem cell.
authors.affiliation: Department of Dermatology, St. Louis University, St. Louis, Missouri 63104, USA. sumyou@hotmail.com
authors.forename: Summer R
authors.initials: SR
authors.lastname: Youker
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Billingsley
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015266:Carcinoma, Merkel Cell / Q000175:diagnosis* / Q000628:therapy; D003937:Diagnosis, Differential; D017809:Fatal Outcome; D051677:Histiocytoma, Malignant Fibrous / Q000175:diagnosis* / Q000628:therapy; D006801:Humans; D007150:Immunohistochemistry; D008048:Lip Neoplasms / Q000175:diagnosis* / Q000628:therapy; D008297:Male