ON THIS PAGE: You will find basic information about this group of diseases and the parts of the body they may affect. This is the first page of Cancer.Net’s Guide to Ovarian, Fallopian Tube, and Peritoneal Cancer. Use the menu to see other pages. Think of that menu as a roadmap for the complete guide.
About the ovaries
The ovaries are part of a woman’s reproductive system. Every woman has two ovaries, with one located on each side of the uterus. They are almond-shaped and about 1.5 inches long. These glands contain germ cells, also called eggs. Ovaries are the primary source of estrogen and progesterone. These hormones influence breast growth, body shape, body hair, and regulate the menstrual cycle and pregnancy. During menopause, the ovaries stop releasing eggs and producing certain hormones.
About the fallopian tubes
The fallopian tubes are part of a woman’s reproductive system. They are small ducts that link a woman’s ovaries to her uterus. Typically, every woman has 2 fallopian tubes, with 1 located on each side of the uterus. During a woman’s monthly ovulation, usually an egg is released from one ovary and travels to the uterus through a fallopian tube.
About the peritoneum
The peritoneum is a tissue that lines the abdomen and most of the organs in the abdomen. The tissue covers the uterus, bladder, rectum, and the ovaries and fallopian tubes. A liquid called peritoneal fluid covers the tissue’s surface. This liquid helps the organs move within the abdomen and prevents them from sticking together.
About ovarian, fallopian tube, and peritoneal cancer
The term “ovarian cancer”' is often used to describe cancers that begin in the cells in the ovary, fallopian tube, and peritoneum. The cancers are closely related and are treated the same way. These types of cancer begin when healthy cells in these areas change and grow out of control, forming a mass called a tumor. A tumor can be cancerous or benign. A cancerous tumor is malignant, meaning it can grow and spread to other parts of the body. A benign tumor means the tumor can grow but will not spread.
Research studies suggest that high-grade serous cancer (HGSC), which accounts for most ovarian cancer, in most cases actually starts in the distal end (fimbria) of the fallopian tubes and spreads to the surface of the ovaries. Based on this understanding, some doctors recommend removal of the fallopian tubes rather than tying or banding the tubes, for when a woman is undergoing surgery for benign disease and does not want to get pregnant in the future.
Because the surfaces of the ovaries and the peritoneum are made up of the same types of cells, the two diseases look alike under a microscope. Peritoneal cancer can still develop after ovaries have been removed. Just as with ovarian cancer, some peritoneal cancers may begin in the fallopian tube.
There can also be noncancerous tumors and cysts in this area of the body. Removing the ovary or the part of the ovary where the tumor is located can successfully treat a noncancerous ovarian tumor. An ovarian cyst forms on the surface of the ovary and is different than a noncancerous tumor. A simple ovarian cyst can occur during a woman’s normal menstrual cycle and usually goes away without treatment. Simple ovarian cysts are not cancerous.
Types of ovarian cancer
Epithelial carcinoma. Epithelial carcinoma makes up 85% to 90% of ovarian cancers.
The main histologic types of epithelial tumors include serous, endometrioid, clear cell, mucinous, mixed tumors, and several rare malignancies, including Brenner and transitional cell cancers.
The vast majority of epithelial cancers are serous, and these cancers are either high-grade serous carcinoma (HGSC) or low-grade serous carcinoma (LGSC).
HGSCs are the most common histologic type of malignancy of the ovary, fallopian tube, and peritoneum, as noted above. LGSC is less common.
Germ cell malignancies. This uncommon type of ovarian cancer  develops in the egg-producing cells of the ovaries. Germ cell malignancies typically occur in females aged 10 to 29 years.
The types of germ cell tumors are dysgerminomas, immature teratoma, and endodermal sinus tumors (called EST and yolk sac tumors), which include embryonal carcinoma.
Stromal malignancies. This rare form of ovarian cancer  develops in the connective tissue cells that hold the ovaries together. This tissue sometimes makes the female hormones estrogen and progesterone. Over 90% of these stromal tumors are granulosa cell tumors, either adult or childhood types.
Granulosa cell tumors may secrete estrogen resulting in unusual vaginal bleeding at the time of diagnosis. Other types are theca cell malignancies, and mixtures of these two types.
Types of fallopian tube cancer
Fallopian tube cancer was once thought to be rare, but we now know that most cancers previously labeled “ovarian cancer” actually begin in a fallopian tube. Most cancers arising in the fallopian tube are epithelial and begin in the distal (outer) end of the tube, near the fimbria, which is where the opening of the tube is located and where eggs released from the ovary must enter in order to be fertilized. Virtually all of these are serous cancers, and most serous cancers are high-grade (HGSC).
Other very rare types of fallopian tube cancer include leiomyosarcoma, which arise from the smooth muscle of the fallopian tube, and transitional cell cancer that arise within other cells that line the fallopian tubes.
Looking for More of an Introduction?
If you would like more of an introduction, explore these related items. Please note these links will take you to other sections on Cancer.Net:
ASCO Answers Fact Sheet: Read a 1-page fact sheet on ovarian cancer  that offers an introduction to this type of cancer. This fact sheet is available as a PDF so it is easy to print out.
Cancer.Net Video: Watch this introduction to ovarian cancer .
The next section in this guide is Statistics . It helps explain the number of women who are diagnosed with this disease and their survival rates. You may use the menu to choose a different section to continue reading in this guide.