Adenoid cystic carcinomas of the breast and salivary glands (or 'The strange case of Dr Jekyll and Mr Hyde' of exocrine gland carcinomas).

Adenoid cystic carcinoma (AdCC) is a tumour with myoepithelial differentiation and characterised by the presence of a dual population of basaloid and luminal cells arranged in specific growth patterns. These tumours, regardless of the anatomical site, are characterised by expression of the proto-oncogene and therapeutic target c-KIT, and seem to harbour a specific chromosomal translocation t(6;9) leading to the fusion gene MYB-NFIB and overexpression of the oncogene MYB. However, the clinical behaviour of salivary gland and breast AdCC differs; while salivary gland lesions have a relatively high proclivity to metastasise, patients with breast AdCCs have an excellent outcome. Here the clinical, morphological and molecular features, and potential therapeutic targets of salivary gland and breast AdCCs are reviewed.