Purpose of review: Ovarian borderline tumours are relatively uncommon, but not rare, neoplasms. Pathologists and oncologists often struggle with various aspects of borderline tumours which are sometimes controversial and poorly understood.
Recent findings: In this review, I discuss pathological and clinical aspects of ovarian borderline tumours of the two most common types, serous and mucinous, these having a different natural behaviour. The recent literature is reviewed as well as important papers prior to this. Controversial aspects covered include the relationship between borderline tumours and carcinomas, the significance of microinvasion, the significance of a micropapillary architecture in serous borderline tumours, the diagnostic criteria for and significance of extraovarian 'implants', lymph node involvement, staging issues and tumour behaviour.
Summary: Ovarian borderline tumours have an excellent prognosis, although a small percentage is associated with the development of progressive disease. It has been suggested that the term borderline tumour should be abandoned but it is argued that this terminology should be retained for both serous and mucinous neoplasms because of the risk of extraovarian implants in serous borderline tumours and the large size and heterogeneity of mucinous borderline tumours which may result in an invasive focus being undetected by the pathologist.