title: Metastasising pleomorphic adenoma: Systematic review.
abstract: BACKGROUND
  Pleomorphic adenoma (PA) is the commonest benign neoplasm of salivary glands.(1) PA can undergo malignant transformation to ex-pleomorphic adenoma (2,3) but rarely, can metastasise without malignant transformation.(4,5) Metastasising pleomorphic adenoma (MPA) is a rare malignant tumour which, histologically, is indistinguishable from PA yet produces secondary tumours in distant sites.(6,7,8) OBJECTIVE: Our aim is to review the literature for all reported cases of MPA and create a virtual series. The age and location of primary tumour with the location and time to metastasise will be reviewed. The prognosis and treatment options will be explored.
  
  
  METHODS
  We conducted a PUBMED search with a combination of keywords: metastasizing/metastasising AND pleomorphic adenoma OR mixed tumour. An author's own case has also been included.
  
  
  RESULTS
  Between 1942 and 2014 there were 80 case reports included in the review, plus the authors own case. Mean age at diagnosis of MPA was 49.5 years (range 11-83). Male-to-female ratio was 34:46. The mean time between PA and MPA was 14.9 years (range 0-51), with three cases reporting simultaneous presentation. 72.8% (n = 59) of cases reported PA local recurrence prior to MPA. The three most common sites for MPA were: bone 36.6% (n = 28), lung 33.8% (n = 26) and neck lymph nodes 20.1% (n = 17). Survival was poorly reported, but 41 (80.4%) were alive at 1-year.
  
  
  CONCLUSIONS
  Benign MPA is rare. Metastasis occurs years after the initial PA and is associated with multiple local recurrences. Histologically, MPA retain their benign nature yet demonstrate malignant behaviour.
authors.affiliation: Department of Medicine, St George's University of London, Cranmer Terrace, London, SW17 0RE, UK. Electronic address: jamesknight@doctors.org.uk.
authors.forename: James
authors.initials: J
authors.lastname: Knight
authors.affiliation: Department of General Surgery, Royal Surrey County Hospital, UK.
authors.forename: Kumaran
authors.initials: K
authors.lastname: Ratnasingham
mesh_terms: D008949:Adenoma, Pleomorphic / Q000175:diagnosis*; D006801:Humans; D009362:Neoplasm Metastasis; D011379:Prognosis; D012468:Salivary Gland Neoplasms / Q000175:diagnosis* / Q000556:secondary*
keywords: Metastasising pleomorphic adenoma; Systematic review