[Mucinous ovarian neoplasms. Prognostically mostly excellent, infrequently a wolf in sheep's clothing]

Mucinous ovarian neoplasms represent the second largest group of epithelial ovarian tumors after serous neoplasms, of which benign cystadenomas constitute more than 80 %. Mucinous cystadenomas and carcinomas cannot be distinguished by the clinical features or the mean age of onset of the disease. They typically occur unilaterally, are confined to the adnexae (FIGO stage I) and clinically present with non-specific abdominal symptoms or are diagnosed by chance. The mean age of disease onset is around 50 years old. The prognosis is excellent. Implants, peritoneal metastases and bilateral occurrence of ovarian mucinous neoplasms should lead to the suspicion of metastasis particularly from a gastrointestinal tumor. Neither microinvasion defined as a maximum extent of invasion of 5 mm, nor intraepithelial carcinoma characterized by high grade atypia without invasion, affect the prognosis of mucinous borderline tumors. Mucinous carcinomas typically show confluent glandular, expansile growth that leads to a labyrinth-like pattern. A destructive infiltrative or nodular growth pattern, however, should lead to the consideration of metastasis. Mural nodules that may reveal a spindle cell sarcomatous or anaplastic carcinomatous pattern occur infrequently in mucinous and do not affect the prognosis. Pax8 positivity is indicative of a primary ovarian neoplasm. In this case, however, mucinous tumors associated with teratomas may show the colonic immunoreaction pattern (CK7-/CK20+/CDX2+). The rare mucinous tumors with endocervical differentiation are now designated as seromucinous tumors and consist of two or more distinct cell types, are frequently associated with endometriosis and seem to show a molecular genetic relationship to endometrioid neoplasms.