Ovarian neoplasms are a heterogeneous group of tumours classified according to morphological and clinical features. The main subgroups are:

• epithelial tumours
• sex cord – stromal tumours
• germ cell tumours
• miscellaneous and metastatic tumours.

The majority of ovarian tumours (59% of all ovarian tumours and up to 90% of all primary ovarian malignancies) are epithelial. Epithelial tumours can be further classified as follows:

• serous
• mucinous
• endometrioid
• mixed mesodermal / carcinosarcoma
• clear cell
• transitional cell
• mixed epithelial
• undifferentiated carcinomas.

The most common tumours are serous and mucinous lesions.

Mixed mesodermal tumours are now considered to be carcinomas with areas of sarcomatous differentiation.

• A benign tumour has no abnormal cytological or proliferative features and no evidence of stromal invasion. There is no significant malignant potential.
• A borderline (low malignant potential or atypically proliferating) tumour is a lesion which has abnormal cytological and proliferative features within its epithelium but which has no evidence of invasion into the stromal supporting tissues. Extraovarian disease can occur and these tumour deposits are referred to as implants. Non-invasive implants are associated with a good prognosis. Invasive implants are associated with a prognosis that is intermediate between those of benign and malignant tumours. Most borderline tumours present as stage I lesions and are cured by surgery. Stage by stage the overall survival of women with borderline tumours is superior to women with epithelial ovarian cancer.
• A malignant tumour is present when there is evidence of invasion into the stromal tissues of the ovary. This is usually associated with cytological atypia and increased proliferative activity. Invasion is best defined as the presence of irregular spiculated or ragged epithelial islands with individual cells extending into the stromal tissues. These stromal tissues can display reactive changes such as necrosis or an immature fibroblastic response. These cytological and proliferative changes can occur focally within the ovarian mass. An ovarian tumour must be adequately sampled for histological examination.
• Primary peritoneal cancer is a tumour which shows similar morphological characteristics toovarian cancer but which has no or minimal ovarian involvement.

GRADING OF OVARIAN CANCER

There is no single universally accepted system for grading ovarian cancers. Many studies have used different systems proposed either by FIGO or WHO or the American Gynecologic Oncology Group (GOG). A newly proposed grading system, based on the Nottingham system of breast cancer grading, assesses the architectural pattern of the ovarian tumour, cytological atypia and the mitotic activity within the tumour.^{179, 180, 181} The FIGO staging system described in Annex 1 is a surgical staging system which does not incorporate the grade of the tumour.

PSEUDOMYXOMA PERITONEI

Pseudomyxoma peritonei is a clinical condition characterised by the presence of mucinous material within the peritoneal cavity. This condition may originate from either the ovary or gastrointestinal tract. In gynaecological pathology it is more often seen in association with borderline mucinous ovarian tumours. In view of the debate about the primary site of origin of these tumours the appendix should be examined. Pathological examination of the mucinous material and associated tissues should specify whether epithelial cells are present or not. The cytological characteristics of the cells should also be described.

BRAC1 AND BRAC2

BRCA1, a gene on chromosome 17 and BRCA2, a gene on chromosome 13, increase susceptibility to breast and ovarian cancer.