Distinction of primary ovarian mucinous tumors and mucinous tumors metastatic to the ovary: A practical approach with guidelines for prediction of primary site for metastases of uncertain origin

The distinction of primary ovarian mucinous tumors from metastatic mucinous carcinomas involving the ovary can be challenging, even for experienced gynecologic pathologists. Metastatic mucinous carcinomas are usually easily recognized as such when they exhibit characteristic features. However, metastases can share gross, microscopic, and immunohistochemical features with primary ovarian mucinous tumors, simulating primary ovarian atypical proliferative (borderline) mucinous tumors of gastrointestinal type and well-differentiated mucinous carcinomas of usual (gastrointestinal or nonspecific) type. General features of metastases in the ovaries and the diagnostic problems posed by them are presented. Characteristic features of primary ovarian mucinous tumors and the more common metastatic carcinomas that can exhibit mucinous differentiation are summarized. Guidelines are offered for synthesizing the combined gross, microscopic, and immunohistochemical features to suggest likely sites of origin for those mucinous tumors in the ovary suspected to be metastases from undiagnosed primary neoplasms.