Ovarian mucinous cystadenocarcinoma, light micrograph. Ovarian mucinous cystadenoma (15-20% of ovarian tumours) is a usually large and benign tumour showing glands and cysts, with filiform papillae with fibrovascular cores, lined by columnar epithelium. Also, minor foci of cellular stratification and mild to moderate atypia may appear (mucinous cystadenoma with focal atypia or focal proliferation).