the cyst fluid has come to be describe the particular type of epithelial cell seen in these tumors may involve the surface of the ovary the division between benign, borderline, and malignant is ascertained by assessing: cellular atypia (whether or not individual cells look abnormal) invasion of surrounding ovarian stroma (whether or not cells are infiltrating surrounding tissue) borderline tumors may have cellular atypia but do NOT have evidence of invasion the presence of psammoma bodies are a characteristic microscopic finding of cystadenocarcinomas Prognosis The prognosis of a serous tumor, like most neoplasms, depends on degree of differentiation this is how closely the tumor cells resemble benign cells a well-differentiated tumor closely resembles benign tumors a poorly differentiated tumor may not resemble the cell type of origin at all a moderately differentiated tumor usually resembles the cell type of origin, but appears frankly malignant extension of tumor to other structures in particular with serous malignancies, the presence of malignant spread to the peritoneum is important with regard to prognosis. The five-year survival rate of borderline tumors and malignant tumors confined to the ovaries are 100% and 70% respectively. If the peritoneum is involved, these rates become 90% and 25%. While the 5-year survival rates of borderline tumors are excellent, this should not be seen as evidence of cure, as recurrences can occur many years later. Mucinous tumors Mucinous tumors: Closely resemble their serous counterparts but unlikely to be bilateral Somewhat less common, accounting for about 25% of all ovarian neoplasms In some cases mucinous tumors are characterized by more cysts of variable size and a rarity of surface involvement as compared to serous tumors Also in comparison to serous tumors, mucinous tumors are less frequently bilateral, approximately 5% of primary mucinous tumors are bilateral. May form very large cystic masses, with recorded weights exceeding 25 kg Pathology Mucinous tumors are characterized by a lining of tall columnar epithelial cells with apical mucin and the absence of cilia, similar in appearance with benign cervical or intestinal epithelia. The appearance can look similar to colonic or ovarian cancer, but typically originates from the appendix (see mucinous adenocarcinoma with clinical condition Pseudomyxoma peritonei). Clear stromal invasion is used to differentiate borderline tumors from malignant tumors. Prognosis 10-year survival rates for borderline tumors contained within the ovary, malignant tumors without invasion, and invasive malignant tumors are greater than 95%, 90%, and 66%, respectively. One