Cancer Types – Ovarian Cancer

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Ovarian Cancer: Overview

Approved by the Cancer.Net Editorial Board, 10/2017

About the ovaries

The ovaries are part of a woman’s reproductive system. Every woman has 2 ovaries, with 1 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 connect 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 1 ovary and travels through a fallopian tube to the uterus.

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 cancers

The term “ovarian cancer”’ is often used to describe cancers that begin in the cells in the ovary,  fallopian tube, or peritoneum. The cancers are closely related and are treated the same way. In this guide, this group of diseases is referred to as “ovarian/fallopian tube cancer” because peritoneal cancer is relatively rare. When the term “ovarian cancer” is used, it includes both fallopian tube and peritoneal cancers, because it may be unclear where the cancer started.

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.

An ovarian cyst forms on the surface of the ovary and it can occur during a woman’s normal menstrual cycle and usually goes away without treatment. Simple ovarian cysts are not cancerous.

Research studies suggest that most ovarian/fallopian tube cancers are high-grade serous cancers (HGSC), and in most cases, the cancer actually starts in the distal, or outer, end of the fallopian tubes and then spreads to the surface of the ovaries and beyond. Based on this new knowledge, some doctors recommend removal of the fallopian tubes rather than tying or banding the tubes for contraception, or when a women is undergoing surgery for benign disease and does not want to get pregnant in the future.This strategy could prevent the development of these cancers in the future.

Because the surfaces of the ovaries, the lining of the fallopian tubes, and the covering cells of the peritoneum are made up of the same types of cells, most of these diseases look alike under a microscope. Peritoneal cancer can still develop after ovaries and fallopian tubes have been removed. Just as with ovarian cancer, some peritoneal cancers may begin in the fallopian tube and spread from the end of the fallopian tubes into the peritoneal cavity.

Types of ovarian and fallopian tube cancer

  • Epithelial carcinoma. Epithelial carcinoma makes up 85% to 90% of ovarian/fallopian tube cancers. The main types of epithelial tumors include serous, endometrioid, clear cell, mucinous, mixed tumors, and several rare malignancies, including Brenner and transitional cell cancers. These types describe how these different ovarian/fallopian tube cancers are classified based on how they look under the microscope. There can be differences in how these cancers behave and which treatments will work best.
    The vast majority of epithelial cancers are serous, meaning they resemble the cells lining the fallopian tube. These cancers are either HGSC or low-grade serous carcinoma (LGSC). HGSCs make up the vast majority of ovarian/fallopian tube cancer. LGSC is uncommon.
  • 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, endodermal sinus tumors (called EST and yolk sac tumors), and embryonal carcinomas.

  • Stromal malignancies. This rare form of ovarian cancer develops in the connective tissue cells, granulosa and theca cells, that hold the ovaries together. This tissue sometimes makes the female hormones estrogen and progesterone. Over 90% of these stromal tumors are called 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 2 types.

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 begin in the 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 are HGSC, although in rare cases, other types of cancer can start in the fallopian tube.

Read more about ovarian cancer here.

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