Metastasising pleomorphic adenoma: Systematic review.

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.

METHOD: 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.

CONCLUSION: 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.