The ovary is a common site of metastatic tumour. In many cases of ovarian metastasis there is a known history of malignancy but in other cases the ovarian tumour is the first manifestation of disease. In this review metastatic colorectal, appendiceal, gastric, breast, pancreatic and biliary tract, hepatocellular, renal, transitional and cervical carcinomas and metastatic malignant melanoma involving the ovary are discussed, as is the issue of synchronous ovarian and endometrial carcinomas. Peritoneal tumours, including primary peritoneal carcinoma, mesothelioma and intra-abdominal desmoplastic small round cell tumour, involving the ovary are also discussed, together with a variety of other rare, metastatic ovarian neoplasms. Many metastatic adenocarcinomas involving the ovary, especially those exhibiting mucinous differentiation, closely mimic primary ovarian adenocarcinomas with morphologically bland areas simulating benign and borderline cystadenoma. This is referred to as a maturation phenomenon. In recent years immunohistochemistry, especially but not exclusively differential cytokeratin (CK7 and CK20) staining, has been widely used as an aid to distinguish between a primary and secondary ovarian adenocarcinoma. While immunohistochemistry undoubtedly has a valuable role to play and is paramount in diagnosis in some cases, the results must be interepreted with caution, especially in mucinous tumours, and within the relevant clinical context. We feel the significance of differential cytokeratin staining is not always understood by histopathologists and this can result in erroneous interpretation. We critically discuss the value of immunohistochemistry and associated pitfalls with each tumour type described.

Most nonuterine high-grade serous carcinomas (HGSCs) in women with hereditary breast and ovarian cancer syndrome, due to germline BRCA1/2 mutation, arise in the fimbria of the fallopian tube. However, the site of origin of sporadic HGSC, which is usually widely disseminated at presentation, is not well established. We sought to characterize cases of HGSC discovered incidentally in patients not known to be at high risk, in order to determine the site distribution and possible origin of sporadic HGSC. Incidental microscopic, non-mass-forming cases of serous tubal intraepithelial carcinoma or HGSC in salpingo-oophorectomy specimens in which the tubes and ovaries had been extensively examined were identified. No patients were known or suspected BRCA1/2 mutation carriers. Twenty-one cases were identified (mean age: 57 y). Surgery was for benign disease (n=15), uterine endometrioid adenocarcinoma or atypical hyperplasia (n=3), bladder carcinoma (n=1), or ovarian serous borderline tumor (n=2). In 16 of 21 cases, the lesion was confined to the fallopian tube (unilateral in 14 cases, bilateral in 2). There was serous tubal intraepithelial carcinoma in all cases and invasive HGSC into the underlying lamina propria in 8 of these 16 cases; the invasive focus measured 1.3 cm or less in every case. In the remaining 5 cases, there was fallopian tube mucosal and ovarian involvement; in 2 of these cases, there was also microscopic peritoneal involvement. Sporadic cases of nonuterine HGSC arise in the fallopian tube fimbria in a large majority of cases, providing further evidence for the tubal origin of these neoplasms.

The revised FIGO 2013 staging for carcinomas of the ovary, fallopian tube and peritoneum has introduced a single system for tumours originating at these sites. The system requires pathologists to assign a primary site (ovary, tube or peritoneum), but does not provide guidance to aid this assignment. This is particularly problematic in cases of advanced-stage (stage II or greater) high-grade serous carcinoma (HGSC), where there is commonly involvement of two or more sites by tumour, and practice among pathologists in determining where a tumour has arisen varies widely. This has significant implications for recording of tumour incidence and mortality, data collection by cancer registries, and entry into clinical trials. We propose guidelines for assigning the primary site of HGSC based on careful macroscopic and histological assessment. The use of these guidelines, in conjunction with the new FIGO staging system, is intended to act as an impetus to promote debate and provide a uniform and consistent approach in assigning primary tumour site which will facilitate comparison of data between centres.