Pathology of primary and metastatic mucinous ovarian neoplasms

Recent years have seen a dramatic change in the pathological approach to ovarian mucinous neoplasms. A substantial proportion of tumours previously considered to be ovarian primaries actually represent secondary ovarian involvement by tumours elsewhere in the body. Two major categories of tumour have completely disappeared from the diagnostic spectrum: ovarian 'borderline' mucinous tumour associated with pseudomyxoma peritonei, and widely disseminated mucinous carcinomas. The emergent picture of true ovarian primary carcinoma of pure mucinous morphology is that this is a rare malignancy that is low grade and low stage at presentation in the vast majority of cases, with a very low likelihood of aggressive clinical behaviour. A large volume of literature has appeared concerning the pathological distinction of primary from metastatic ovarian mucinous neoplasms in view of the dramatically different prognosis and treacherously similar morphology. Clinicopathological parameters useful in the distinction of primary from metastatic mucinous ovarian carcinomas are reviewed. Major features favouring metastases are bilaterality, size < 10 cm, surface involvement, extensive intra-abdominal spread and an extensive infiltrative pattern with desmoplasia. Two morphological patterns essentially exclude ovarian origin: colloid and signet ring carcinomas. Features favouring primary ovarian origin are unilaterality, large size > 12 cm, smooth external surface and association with other ovarian pathology. An admixture of benign, borderline and malignant patterns in the same tumour favour primary origin, but can be misleading as a 'maturation' pattern in metastases can result in the same appearance.