Non-epithelial ovarian tumours: a review of selected patterns that mimic epithelial tumours and other high-grade malignancies

Non-epithelial ovarian tumours exhibit a diverse array of growth patterns that can mimic epithelial ovarian cancers or other high-grade malignancies. This review highlights selected morphologic features that may assist in the differential diagnosis, as well as recent advances in immunohistochemistry. Steroidogenic factor-1 is a novel marker for sex cord-stromal differentiation and is useful in the diagnosis of granulosa cell tumour. SALL4 is a novel marker of primitive germ cell tumours and is useful in the diagnosis of yolk sac tumour. Distinction of primary versus metastatic origin of carcinoid tumour is important and gross and microscopic features are more accurate to this end than immunohistochemistry, except for the value of TTF-1 in pulmonary or cervical neuroendocrine tumours. Finally, unusual presentations of struma ovarii are also discussed, including proliferative struma, extra-ovarian struma, and carcinoma arising within struma ovarii.