Cancerous tumours of the ovary

A cancerous tumour of the ovary can grow into and destroy nearby tissue. It can also spread (metastasize) to other parts of the body. Cancerous tumours are also called malignant tumours. Cancerous ovarian tumours are grouped by the type of cells that the cancer starts in.

Epithelial tumours

Epithelial tumours start in epithelial cells, which make up the outer layer of the ovary (called the epithelium). Cancerous epithelial tumours are also called epithelial ovarian carcinomas, and the different types have carcinoma as part of their name. Most ovarian cancers are epithelial ovarian carcinomas. It 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 cancerous epithelial tumour. It can occur in both ovaries, and tumours can range in size from small to quite large. Serous carcinomas are either high grade (HGSC) or low grade (LGSC). HGSC is more common than LGSC. This cancer is usually diagnosed at a later stage. Many HGSC are now thought to come from cells from the nearby fallopian tube that have implanted on the surface of the ovary.

Other epithelial tumours

These less common tumours also start in the epithelial cells:

Mucinous carcinoma usually occurs in one ovary and can grow to be very large. Most tumours are diagnosed at an early stage. Mucinous carcinoma that has started in the ovary can be hard to tell apart from cancer that has spread (metastasized) from another part of the body to the ovary.

Endometrioid carcinoma is linked to endometriosis in 10% to 40% of cases. Endometriosis is a non-cancerous condition in which endometrial-type tissue (similar to the inner lining of the uterus) can grow into areas of the body other than the uterus, including the ovaries. These tumours can occur in both ovaries and grow to a large size.

Clear cell carcinoma is linked to endometriosis in at least 50% of cases. They are more commonly diagnosed at an early stage as compared to serous carcinoma, but are likewise considered high-grade tumours.

Mixed carcinomas are made up of more than one type of cell. A common combination is clear cell carcinoma mixed with endometrioid carcinoma. Both cell types are linked to endometriosis.

Undifferentiated carcinoma refers to tumours that start in epithelial cells but cannot be grouped into any type of epithelial ovarian carcinoma. This is because the cells no longer resemble those of the other types. They tend to grow and spread more quickly than the other types of epithelial ovarian carcinoma.

Malignant mesodermal mixed tumours (also called carcinosarcoma or MMMT) grow quickly and are usually large. This cancer is usually diagnosed at a later stage.

Borderline ovarian tumours

Borderline ovarian tumours tend to develop in women at a younger age than most ovarian cancers. They occur most often in women from age 39 to 45. They may occur in one or both ovaries.

Doctors may not classify borderline tumours as cancer because they grow differently from typical ovarian cancers (carcinomas). The tumour cells usually don’t grow into nearby tissue as cancer cells normally do. If they spread outside the ovary into the abdominal cavity, they may implant on the lining of the abdomen but not grow into it. They grow slowly and most are stage 1 at diagnosis.

These tumours are also known as tumours of low malignant potential, tumours of borderline malignancy, atypical proliferative tumours or borderline epithelial ovarian tumours.

Serous borderline tumours are most often in both ovaries.

Mucinous borderline tumours are either endocervical-type or intestinal-type. The endocervical-type tumours are less common, but more commonly may be in both ovaries. The intestinal-type tumours are large and usually found in one ovary.

Endometrioid borderline tumours, clear cell borderline tumours and Brenner (transitional cell) borderline tumours are almost always found in one ovary.

Stromal tumours

Stromal tumours (also called sex cord stromal tumours) start in the cells of the stromal tissues that support the ovary. These cells produce sex hormones, such as estrogen, progesterone and androgens. Stromal tumours often produce too much of these hormones.

Stromal tumours make up about 7% of all cancerous ovarian tumours. Most are low grade. Most stromal tumours are diagnosed in women older than 50 years of age, but they may occur in adolescents and young women as well.

Granulosa cell tumours are the most common type of malignant stromal tumours. Most of these tumours are stage I at the time of diagnosis. They vary in size and can be solid or contain cysts.

  • Adult granulosa cell tumours can occur at any age but are most common in perimenopausal women.
  • Juvenile granulosa cell tumours tend to develop in one ovary and occur most often in girls and women under the age of 30.

Other stromal tumours

These types of stromal tumours are less common:

Sertoli-stromal cell tumours may contain only Sertoli cells (Sertoli cell tumour) or both Sertoli and Leydig cells (Sertoli-Leydig cell tumour). Sertoli-stromal cell tumours are usually diagnosed in young women. The average age at diagnosis of Sertoli and Sertoli-Leydig tumours is 30 and 25 respectively. Sertoli-Leydig tumours may produce androgens, which cause male characteristics such as facial hair and a deepened voice.

Sex cord tumour with annular tubules (SCTAT) represents a separate category of stromal tumour. Experts disagree about whether they are more closely related to granulosa cell tumours or Sertoli-Leydig tumours. There are 2 subtypes of SCTAT tumours:

  • One type is linked to Peutz-Jeghers syndrome. Tumours often develop in both ovaries. They can be cancerous, but they usually are non-cancerous.
  • The other type is not associated with Peutz-Jeghers syndrome. Tumours are larger and are more often cancerous.

Gynandroblastomas are large tumours composed of granulosa cells and Sertoli cells. It is not known which type of cell they start from.

Steroid cell tumours are composed of cells resembling steroid-hormone secreting cells. Stromal luteoma and Leydig cell tumours are clinically benign. Steroid cell tumours, not otherwise specified, are clinically malignant in approximately 1/3 of cases.

Fibrosarcomas are high-grade, aggressive tumours. They are usually large and affect one ovary.

Germ cell tumours

Germ cell tumours start in the cells that make the eggs (called germ cells) in the ovary. These tumours account for 2% to 3% of all ovarian cancers. Most germ cell tumours are only in the ovary at the time of diagnosis. They usually develop in young women in their teens and 20s.

Dysgerminomas are the most common cancerous ovarian germ cell tumour. There is spread within the abdomen and pelvis (called extraovarian spread) at the time of diagnosis in a third of cases. In approximately 20% of cases, tumours are in both ovaries.

Yolk sac tumours (endodermal sinus tumours) account for approximately 20% of cancerous ovarian germ cell tumours. Extraovarian spread is found in half of the cases at the time of diagnosis. It is rarely seen in both ovaries in stage I.

Immature teratomas are made up of cancer cells that look like cells from a developing embryo. Immature teratomas are usually found in one ovary but may spread to the other ovary. Immature teratomas are most often found in girls or young women under the age of 20.

Other germ cell tumours

These types of germ cell tumour are very rare:

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.

Embryonal carcinoma is usually seen as part of a mixed germ cell tumour. The tumour can be found in the ovary but more often in the testicle.

Polyembryoma is often found as part of a mixed germ cell tumour.

Choriocarcinomaof the ovary (nongestational) is most often found as part of a mixed germ cell tumour. Choriocarcinoma is composed of trophoblast, the same type of cells that form the placenta during pregnancy.

Small cell carcinoma of the ovary (hypercalcemic type) is a high-grade tumour that is associated with higher than normal amounts of calcium in the blood (hypercalcemia).

Peritoneal carcinomas

Peritoneal carcinomas are closely related to epithelial ovarian cancer but start in the peritoneum. The types of tumour cells are similar to those found in the ovary, but there is very little or no cancer in the ovary, and it isn’t clear where the cancer started. A subset of peritoneal-based carcinomas is frequently associated with endometriosis (e.g. endometrioid carcinoma, clear cell carcinoma).

Primary peritoneal serous carcinomas

High-grade peritoneal serous carcinoma (also referred to as primary peritoneal serous carcinoma) will usually have multiple tumours along the surfaces of many organs in the abdomen and pelvis at the time of diagnosis.

The following criteria are used to diagnose a primary peritoneal serous carcinoma and tell it apart from epithelial ovarian serous carcinoma.

  • The ovaries are normal in size, are enlarged by a benign growth or were previously removed.
  • There is more cancer in the abdomen and pelvis than on the surface of either ovary.
  • Tumours on the ovary are no more than 5 x 5 mm.
  • The tumours are made up mostly of serous cells (cells that produce fluid).

Expert review and references

  • American Cancer Society. Ovarian Cancer. 2014:
  • American Society of Clinical Oncology. Ovarian, Fallopian Tube, and Peritoneal Cancer. 2016:
  • Brown J, Jhingran A, Deavers M . Stromal tumors of the ovary. Raghavan D, Blanke CD, Honson DH, et al (eds.). Textbook of Uncommon Cancer. 4th ed. Wiley Blackwell; 2012: 36: 508-518.
  • Clement PD & Young RH. Atlas of Gynecologic Surgical Pathology. 3rd ed. Saunders Elsevier; 2014.
  • Eskander RN, Diaz-Montes TP, Vang R, Armstrong DK, Bristow RE . Borderline tumors and other rare epithelial tumors of the ovary. Raghavan D, Blanke CD, Honson DH, et al (eds.). Textbook of Uncommon Cancer. 4th ed. Wiley Blackwell; 2012: 35: 497-506.
  • Levine DA, Dizon DS, Yashar CM, Barakat RR, Berchuch A, Markman M, Randall ME. Handbook for Principles and Practice of Gynecologic Oncology. 2nd ed. Philadelphia, PA: Wolters Kluwer; 2015.
  • Matei DE, Schilder JM, Michael H . Germ cell tumors of the ovary. Raghavan D, Blanke CD, Honson DH, et al (eds.). Textbook of Uncommon Cancer. 4th ed. Wiley Blackwell; 2012: 37: 520-530.
  • National Cancer Institute. Ovarian Germ Cell Tumors Cancer Treatment for Health Professionals (PDQ®). 2016:
  • Selman AE, Copeland LJ . Extraovarian primary peritoneal carcinomas. Raghavan D, Blanke CD, Honson DH, et al (eds.). Textbook of Uncommon Cancer. 4th ed. Wiley Blackwell; 2012: 34: 485-495.

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