title: Metastatic acinic cell carcinoma in a neurofibroma mistaken for carcinosarcoma.
abstract: BACKGROUND
  Tumor-to-tumor metastasis is a rare, but well-recognized, entity most commonly involving metastatic carcinoma to a mesenchymal neoplasm. We report a case of acinic cell carcinoma of the parotid gland metastatic to a neurofibroma.
  
  
  RESULTS
  A 55-year-old man with a history of a high-grade acinic cell carcinoma of the parotid was seen with a mass at the surgical site and metastatic foci in the scalp 10 months postoperatively. The resection specimen revealed a spindle cell lesion with metastatic foci of high-grade adenocarcinoma, initially diagnosed as a carcinosarcoma. The bland morphology and S-100-positive expression of the spindle cell lesion confirmed the diagnosis of neurofibroma. The high-grade features of the carcinomatous foci and their similarity to the primary tumor confirmed the presence of a tumor-to-tumor metastasis.
  
  
  CONCLUSIONS
  To our knowledge, this is the first reported case of acinic cell carcinoma metastatic to a neurofibroma, an important entity in the differential diagnosis of biphasic tumors of the head and neck.
authors.affiliation: Department of Pathology, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Blvd, Unit 85, Houston, TX 77030, USA.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Cohn
authors.forename: Danielle D
authors.initials: DD
authors.lastname: Elliott
authors.forename: Adel K
authors.initials: AK
authors.lastname: El-Naggar
mesh_terms: D018267:Carcinoma, Acinar Cell / Q000473:pathology*; D002296:Carcinosarcoma / Q000473:pathology*; D003937:Diagnosis, Differential; D004431:Ear, External / Q000473:pathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009378:Neoplasms, Multiple Primary / Q000473:pathology*; D009455:Neurofibroma / Q000473:pathology*; D010307:Parotid Neoplasms / Q000473:pathology*; D012468:Salivary Gland Neoplasms / Q000473:pathology*; D012983:Soft Tissue Neoplasms / Q000473:pathology; D013701:Temporal Bone / Q000473:pathology