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Types of Cancer > Gynecologic Cancers > Ovarian Cancer > Overview

Ovarian Cancer: The Basics

Christopher Dolinsky, MD and Carolyn Vachani, MSN, RN, AOCN
Affiliation: Abramson Cancer Center of the University of Pennsylvania
Last Modified: March 6, 2008

What is the ovary?

The ovaries are two small organs that only women possess. They are located in a woman's pelvis, on each side of her uterus (the organ where a baby grows and develops when a woman is pregnant). The ovaries are each about the size of a peanut M&M, and they can often be felt by your doctor during the bi-manual portion of a pelvic examination. A woman's ovaries are responsible for two important functions in her body: they produce female hormones and they produce eggs. Every month that a woman is fertile and not pregnant, her ovaries release a mature egg that travels into her uterus and has the potential to become fertilized. The ovaries also produce important hormones, namely estrogen and progesterone, which regulate a woman's menstrual cycles, influence the development of a woman's body during puberty, and keep a woman fertile.

What is ovarian cancer?

Ovarian cancer develops when cells in the ovaries begin to grow in an uncontrolled fashion and then invade nearby tissues or spread throughout the body. Large collections of this "out-of-control" tissue are often referred to as tumors. However, some tumors are not really cancer because they cannot spread or threaten someone's life. These are called benign tumors or masses. The tumors that can spread throughout the body or invade nearby tissues represent true invasive cancer, and are called malignant tumors. The distinction between benign and malignant tumors is very important in ovarian cancer because many ovarian tumors are benign. Also, sometimes women (especially young women) can get ovarian cysts, which are collections of fluid in the ovaries that can occasionally grow large or become painful. However, ovarian cysts are not cancerous and should not be confused with ovarian cancer. Your doctor may suggest that you have an ovarian cyst removed if it is becoming bothersome.

Cancers are characterized by the cells from which they originally form. The most common type of ovarian cancer is called epithelial ovarian cancer; it comes from cells that lie on the surface of the ovary known as epithelial cells. Epithelial ovarian cancer comprises about 90% of all ovarian cancers and usually occurs in older women. About 5% of ovarian cancers are called germ cell ovarian cancers and arise from the ovarian cells that produce eggs. Germ cell ovarian cancers are more likely to affect younger women. Another 5% of ovarian cancers are known as stromal ovarian cancers and develop from the cells in the ovary that hold the ovary together and produce hormones. These tumors can create symptoms by producing a large excess of female hormones. Each of these three types of ovarian cancer (epithelial, germ cell, stromal) contains many different subtypes of cancer that are distinguished based on how the cells look under a microscope. Discuss the exact category of ovarian cancer that you have with your physician so that you can get a sense of the particulars of your case.

A rare type of cancer, called primary peritoneal cancer, is a malignant tumor arising from the peritoneum, the lining of the abdominal cavity. It tends to behave in a fashion very similar to ovarian cancer, and they can look identical under the microscope. The treatments used are often the same as those used for ovarian cancer. This type of cancer can develop in women with intact ovaries or in those who have had their ovaries removed.

Am I at risk for ovarian cancer?

As women get older, their risk of developing ovarian cancer increases. In the U.S., it was estimated that 21,650 women would develop ovarian cancer in 2008; and 15,520 women would die of ovarian cancer in 2008. Ovarian cancer accounts for 3% of all cancers in women, and is the 5th most common cause of cancer death for women in the U.S. Unfortunately, the majority of cases of ovarian cancer are found when it is somewhat advanced, because early stage ovarian cancers rarely cause any symptoms. There is some good news, however. From 1985 to 2002 (the most recent statistic years available), the incidence of ovarian cancer decreased by 0.7% per year.

Although there are several known risk factors for getting ovarian cancer, no one knows exactly why one woman gets it and another does not. The most significant risk factor for developing ovarian cancer is age; the older a woman is, the higher her chances are of having it. The majority of ovarian cancers are diagnosed in women after they have gone through menopause, in their late fifties and sixties. The average age for a woman to get a sporadic ovarian cancer (meaning not part of a familial syndrome) is 63 years old, although women with genetic or familial risk factors tend to get ovarian cancer at a slightly younger age (average age of diagnosis is 54 years). Less than 15% of ovarian cancers are diagnosed in women under age 50. Many of these cases are not epithelial (the most common type) and are not amenable to screening with CA125.

Other than age, the next most important risk factor for ovarian cancer is a family history of ovarian cancer, particularly if your family members are affected at an early age. If your mother, sister, or daughters have had ovarian cancer, then you have an increased risk for development of the disease. Scientists estimate that 7% to 10% of all ovarian cancers are the result of hereditary genetic syndromes. Genetic mutations for ovarian cancer have become a hot topic of research lately. Currently, there are three genetic syndromes that are recognized to increase ovarian cancer risk: ovarian cancers associated with colon and endometrial cancers (called hereditary nonpolyposis colorectal cancer syndrome - HNPCC), breast and ovarian cancer syndrome (associated with mutations in either the gene BRCA1 or the gene BRCA2), and site-specific ovarian cancer syndrome (which produces an increased risk for ovarian cancer alone). Women can inherit these mutations from their parents, and it may be worth testing for mutations if a woman has a particularly strong family history of breast or ovarian cancer (meaning multiple relatives affected, especially if they are under 50 years old when they get the disease). Having a mutation doesn't necessarily mean a woman is going to get the disease, but it does greatly increase her chances above the general population. Family members may elect to be tested to see if they carry mutations as well. If a woman does have the mutation, she can get more rigorous screening, take preventive medications, or undergo prophylactic oophorectomies (preventive removal of your ovaries) to decrease her chances of contracting cancer. The decision to get tested is a highly personal one that should be discussed with a doctor who is trained in counseling patients about genetic testing, known as a genetic counselor.

The rest of the risk factors for ovarian cancer are not as significant as age and family history/genetic syndromes, but are mentioned because some of them can be controlled. It appears that the more menstrual cycles (and thus ovulations) a woman has in her lifetime, the more likely she is to develop ovarian cancer. Thus women who started menstruating early, go through menopause late, don't have any children (or have children after age 30), don't use a form of birth control that stops menstruation/ovulation (like birth control pills), and/or who don't breastfeed are all more likely to develop ovarian cancer. It also appears that having a tubal ligation (having your tubes tied) and/or a hysterectomy (having your uterus surgically removed) decreases your risk of ovarian cancer. Prolonged use of the infertility drug, clomiphene citrate, without getting pregnant can also slightly increase a woman's risk for ovarian cancer. Finally, it has been suggested that a diet high in animal fats can increase your risk for ovarian cancer. Remember that all risk factors are based on probabilities, and even someone without any risk factors can still get ovarian cancer. Talk to your doctor about your risk factors for ovarian cancer to understand his/her recommendations for screening and prevention.