Olivia Craig1,2,4, Abhimanyu Nigam1,2,4, Genevieve V. Dall3 and Kylie Gorringe1,2 1Department of Laboratory Research, Peter MacCallum Cancer Centre, Melbourne, VIC 3000, Australia 2The Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, VIC 3010, Australia 3University of Melbourne, Parkville, VIC 3010, Australia Correspondence: kylie.gorringepetermac.org

↵4 These authors contributed equally to this work.

The ovarian epithelial cancer histotypes can be divided into common and rare types. Common types include high-grade serous ovarian carcinomas and the endometriosis-associated cancers, endometrioid and clear-cell carcinomas. The less common histotypes are mucinous and low-grade serous, each comprising less than 10% of all epithelial carcinomas. Although histologically and epidemiologically distinct from each other, these histotypes share some genetic and natural history features that distinguish them from the more common types. In this review, we will consider the similarities and differences of these rare histological types, and the clinical challenges they pose.