Mucinous Neoplasms of the Ovary

Primary mucinous tumors represent 15 % of all ovarian tumors and are classified as either benign, borderline, or malignant. More than 80 % of mucinous tumors are benign, while only 2–7 % are malignant. An overwhelming majority of tumors show gastrointestinal differentiation. Those of Müllerian differentiation are more commonly borderline tumors and rarely benign or malignant. Distinction between intestinal- and Müllerian-type carcinomas may not always be easy, owing to tumor heterogeneity and the fact that some tumors are mixed, such that components of benign, borderline, and carcinoma often coexist within an individual lesion. The diagnostic difficulty is further compounded by the fact that some tumors do not fit agreeably into the three biologic subcategories. Benign tumors containing <10 % of borderline features have been designated cystadenomas with focal atypia or focal proliferation. They are biologically benign. Borderline tumors have mild-to-moderate cytologic atypia, and almost all are followed by an uneventful outcome. In those with severe atypia and a complex architecture but without stromal invasion, the term mucinous borderline tumor with intraepithelial carcinoma is used. These latter tumors have a very low risk of recurrence. Microinvasion refers to borderline tumors, whether with or without intraepithelial carcinoma, that have ≥1 foci of tumor cells infiltrating the stroma but with each focus