Malignant tumours of the ovary are cancerous growths that have the potential to spread (metastasize) to other parts of the body. Malignant ovarian tumours are grouped by the type of cells that the cancer starts in.
Epithelial tumours start in epithelial cells, which make up the outer layer of the ovary (called the epithelium). Malignant epithelial tumours are called epithelial ovarian carcinomas. Approximately 85%–90% of ovarian cancers are epithelial ovarian carcinomas. This is the type of cancer that is most commonly called “ovarian cancer.” These tumours are found most often in women over the age of 50.
- Serous carcinoma is the most common type of ovarian cancer. It can occur in both ovaries and can range in size from small to quite large. This cancer is usually diagnosed at a later stage.
- Mucinous carcinoma usually occurs in one ovary and can grow very large. Most tumours are diagnosed at an early stage. Primary mucinous carcinomas are often difficult to tell apart from cancer that has spread (metastasized) to the ovary from another part of the body.
- Endometrioid carcinoma can occur in both ovaries and grow to a large size. Between 10% and 40% of endometrioid tumours are associated with endometriosis, a disease in which the endometrium (inner lining of the uterus) grows in areas of the body other than the uterus.
- Clear cell carcinoma is uncommon. About half of the cases of clear cell carcinoma are associated with endometriosis.
- Mixed carcinomas are made up of more than one type of cell. At least 10% of the cells in these tumours are a different type of cell. A common combination is mixed clear cell and endometrioid carcinoma. Both cell types are related to endometriosis.
- Carcinosarcoma (malignant mixed mesodermal tumour, or MMMT) is a rare tumour that accounts for less than 1% of all ovarian tumours. These tumours grow quickly and are usually large. This cancer is usually diagnosed at a later stage.
- Undifferentiated carcinoma refers to tumours that are so poorly differentiated (they don’t look like normal cells when viewed under a microscope) that they cannot be grouped into any type of epithelial ovarian carcinoma.
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Stromal tumours (also called sex cord stromal tumours) start in the cells of the stromal tissues that support the ovary. These cells produce sex hormoneshormonesA substance that regulates specific body functions, such as metabolism, growth and reproduction., such as estrogen, progesterone and androgens. Stromal tumours often produce too much of these hormones. Most are low grade (the cancer cells look and act like normal cells and the tumours grow and spread slowly). They make up about 7% of all malignant ovarian tumours. Most stromal tumours are diagnosed in women younger than 40 years of age, and many occur in adolescents and young women.
- Granulosa cell tumours account for about 90% of all stromal ovarian tumours. Most of these tumours develop during the reproductive years.
- Adult granulosa cell tumours account for most granulosa cell tumours. They can occur at any age but are most common in perimenopausal women.
- Juvenile granulosa cell tumours account for about 5% of all granulosa cell tumours. They tend to develop in one ovary and occur most often in adolescents and teenagers.
- Sertoli-stromal cell tumours (also known as androblastomas) are commonly called Sertoli-Leydig tumours. These are rare tumours, accounting for less than 1% of all ovarian tumours.
- The tumours may contain only Sertoli cells or both Sertoli and Leydig cells.
- Pure Sertoli tumours are usually diagnosed in young women and Sertoli-Leydig tumours tend to occur during the teens and 20s.
- Sertoli-Leydig tumours may cause a woman to develop male characteristics, such as facial hair and a deepened voice.
- Sex cord tumours with annular tubules (SCTAT) are uncommon. They represent a separate category of tumour, and experts disagree about whether they are more closely related to granulosa cell tumours or Sertoli-Leydig tumours. There are 2 subgoups of SCTAT tumours:
- One subgroup is associated with Peutz-Jeghers syndromePeutz-Jeghers syndromeA genetic condition that causes dark spots on the mouth and fingers and polyps in the large and small intestine.. The tumours are usually benign and multifocal (occur in more than one place) and develop in both ovaries.
- The other subgroup is not associated with Peutz-Jeghers syndrome. These tumours are larger and are more often malignant.
- Gynandroblastomas are large tumours made up of components of granulosa cells and Sertoli cells. It is unknown which type of cell they start from. Gynandroblastomas are rare, accounting for less than 1% of all ovarian stromal tumours. They are seen most often in woman between the ages of 20 and 50.
- Steroid (lipid) cell tumours are rare. They account for less than 0.1% of all ovarian tumours. These tumours are divided into 3 different types based on the cell they develop from and what the cancer cells look like under a microscope.
- Stromal luteoma and Leydig cell tumour types are benign.
- Steroid cell tumours not otherwise specified can be malignant and aggressive. They appear at an average age of 43 years, are larger than benign steroid cell tumours and may develop in both ovaries.
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Germ cell tumours start in the cells that make the eggs (called germ cells) in the ovary. These tumours account for 2%–3% of all ovarian cancers. They usually develop in young women in their teens and 20s.
- Dysgerminoma is rare, but it is the most common malignant ovarian germ cell tumour. They are low-grade tumours (the cancer cells look and act like normal cells and the tumours grow and spread slowly). They may occur in both ovaries.
- Yolk sac tumours (endodermal sinus tumours) are the second most common ovarian germ cell tumour. They are high-grade tumours (the cancer cells don’t look and act like normal cells and the tumours grow and spread quickly). They develop in one ovary and are usually large.
- Embryonal carcinoma is rarely seen in the ovary (it occurs more often in the testicle). It is usually seen as part of a mixed germ cell tumour.
- Polyembryoma is a very rare tumour that is often found as part of a mixed germ cell tumour.
- Choriocarcinoma of the ovary is rare. It is most often found as part of a mixed germ cell tumour.
- Mixed germ cell tumours contain 2 or more different types of germ cell tumour cells. The most common combination is dysgerminoma and yolk sac tumour cells. These tumours are much less common in the ovary than in the testicle. They account for about 8% of ovarian germ cell tumours.
- Immature teratomas are made up of cancer cells that look like cells from a developing embryo. They are uncommon, accounting for about 3% of all teratomas (mature teratomas are benign). Immature teratomas are most often found in girls under the age of 18.
- Small cell carcinoma of the ovary is a very rare, high-grade tumour that is associated with hypercalcemia (higher than normal amounts of calcium in the blood).
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Extra-ovarian primary peritoneal carcinoma (also called primary peritoneal carcinoma or serous surface papillary carcinoma) is a rare, usually aggressive cancer that starts in the peritoneumperitoneumThe membrane that lines the walls of the abdomen and pelvis (parietal peritoneum), and covers and supports most of the abdominal organs (visceral peritoneum).. It is similar to epithelial ovarian carcinoma except that there is very little or no cancer in the ovary and it isn’t clear where the cancer started.
- Extra-ovarian primary peritoneal carcinoma spreads throughout the abdomen. Multiple tumours can be found on many organs in the abdomen and pelvis, including the omentumomentumA fold in the peritoneum (the membrane that lines the walls of the abdomen and pelvis) that covers and supports organs and blood vessels in the abdomen. and the diaphragmdiaphragmThe thin muscle below the lungs and heart that separates the chest cavity from the abdomen.. Almost all women diagnosed with extra-ovarian primary peritoneal carcinoma will have widespread disease at the time of diagnosis.
- Serous borderline tumours and serous psammocarcinoma of the peritoneum are less aggressive types of extra-ovarian primary peritoneal carcinoma.
- Rare types of extra-ovarian primary peritoneal carcinoma include:
- clear cell
- malignant Mullerian tumour
- Brenner tumour – usually benign
- The following criteria are used to diagnose an extra-ovarian primary peritoneal carcinoma and tell it apart from epithelial ovarian carcinoma.
- The ovaries are normal in size or not present because they were previously removed.
- The amount of cancer in the abdomen and pelvis is greater than that found on the surface of either ovary.
- The tumour did not start in the ovary (it looks like the cancer implanted itself on the surface of the ovary). The tumour doesn’t go deeper than 5 mm into the ovary.
- The cells of the tumour are made up mostly of serous cells (cells that produce fluid).
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