Ovarian carcinomas of epithelial type comprise a heterogeneous group of neoplasms, each with a different underlying pathogenesis and natural behaviour. Accurate classification of ovarian carcinomas is important since each type may be associated with a different behaviour, natural history and outcome. Precise classification is also critical to determine whether alternative therapeutic strategies are appropriate for different tumour types. Previous studies have shown significant interobserver variation in the typing of ovarian carcinomas. There are several areas where there are particular difficulties; these include the distinction between high-grade serous and endometrioid adenocarcinomas and the distinction between a true clear cell carcinoma and clear cell areas within other adenocarcinomas. This review details my approach to the typing of ovarian carcinomas. Morphological assessment, which remains the mainstay in diagnosis, can be supplemented by immunohistochemistry which, for example, is useful in the distinction between serous carcinomas (WT1 positive) and other carcinomas (generally WT1 negative). In recent years, there has been emerging new information regarding the major underlying molecular events in several types of ovarian carcinoma. This has resulted in the acceptance that there are two distinct types of ovarian serous carcinoma. These are termed low-grade and high-grade serous carcinoma, but represent two distinct tumour types rather than low-grade and high-grade variants of the same neoplasm. The integration of clinical, morphological and molecular data has resulted in a more precise classification of ovarian carcinomas and has resulted in the proposal for a broad dualistic pathway of ovarian epithelial carcinogenesis with, in general, low-grade type 1 tumours evolving from benign and borderline neoplasms through a well-defined adenoma-carcinoma sequence, and high-grade type 2 neoplasms arising from an, as yet, undefined precursor lesion.Ovarian carcinomas of epithelial type comprise a heterogeneous group of neoplasms. The major types of primary ovarian epithelial malignancy 1 are listed in the box. Each tumour type has a different underlying pathogenesis and natural behaviour. Although, currently, management of ovarian carcinoma is largely dependent on factors such as tumour grade and stage, and not usually on cell type, it is important to accurately type ovarian carcinomas to ascertain whether the various neoplasms have a different behaviour independent of stage and other clinicopathological parameters. Typing is also important since some tumours, such as mucinous and clear cell carcinoma, seem to exhibit a poor response to platinum-based chemotherapy. 2 In fact, tumour type may be a more reliable predictor of response to chemotherapy than tumour grade.
2This review details my thoughts on and approach to the typing of ovarian carcinomas and is meant as a guide to the practising surgical pathologist. Morphology remains the mainstay in diagnosis but immunohistochemistry may be of value as a...