rare but noteworthy condition associated with mucinous ovarian neoplasms is pseudomyxoma peritonei. As primary ovarian mucinous tumors are usually unilateral (in one ovary), the presentation of bilateral mucinous tumors requires exclusion of a non-ovarian origin, usually the appendix. Endometrioid tumors Endometrioid tumors account for approximately 20% of all ovarian cancers and are mostly malignant (endometroid carcinomas). They are made of tubular glands bearing a close resemblance to benign or malignant endometrium. 15-30% of endometrioid carcinomas occur in individuals with carcinoma of the endometrium, and these patients have a better prognosis. They appear similar to other surface epithelial-stromal tumors, with solid and cystic areas. 40% of these tumors are bilateral, when bilateral, metastases is often present. Pathology Glands bearing a strong resemblance to endometrial-type glands Benign tumors have mature-appearing glands in a fibrous stroma Borderline tumors have a complex branching pattern without stromal invasion Carcinomas (malignant tumors) have invasive glands with crowded, atypical cells, frequent mitoses. With poorer differentiation, the tumor becomes more solid. Prognosis Prognosis again is dependent on the spread of the tumor, as well as how differentiated the tumor appears. The overall prognosis is somewhat worse than for serous or mucinous tumors, and the 5-year survival rate for patients with tumors confined to the ovary is approximately 75%. Clear cell tumors Clear cell tumors are characterized by large epithelial cells with abundant clear cytoplasm and may be seen in association with endometriosis or endometrioid carcinoma of the ovary, bearing a resemblance to clear cell carcinoma of the endometrium. They may be predominantly solid or cystic. If solid, the clear cells tend to be arranged in sheets or tubules. In the cystic variety, the neoplastic cells make up the cyst lining. Prognosis These tumors tend to be aggressive, the five year survival rate for tumors confined to the ovaries is approximately 65%. If the tumor has spread beyond the ovary at diagnosis, the prognosis is poor Brenner tumor Brenner tumors are uncommon surface-epithelial stromal cell tumors in which the epithelial cell (which defines these tumors) is a transitional cell. These are similar in appearance to bladder epithelia. The tumors may be very small to very large, and may be solid or cystic. Histologically, the tumor consists of nests of the aforementioned transitional cells within surrounding tissue that resembles normal ovary. Brenner tumors may be benign or malignant, depending on whether the tumor cells invade the surrounding tissue. Small cell