Ovarian cancer is the fifth leading cause of cancer death in women. Each year in the United States, about 22,000 women are diagnosed with ovarian cancer. About 14,000 American women die each year from this disease.
Certain factors increase the risk for ovarian cancer, while other factors reduce risk. Inherited genetic mutations of BRCA genes are the strongest risk factor. A family history of breast or ovarian cancer is also a strong risk factor.
Many of the preventive factors are related to the number of times a woman ovulates during her lifetime, which is indicated by the number of menstrual periods she has. Fewer menstrual periods and ovulations appear to be associated with reduced risk for ovarian cancer.
Risk Factors for Ovarian Cancer
Older women have a higher risk for ovarian cancer than younger women. Ovarian cancer usually occurs after menopause, although it can develop in women of all ages. Most women diagnosed with ovarian cancer are older than age 55.
Ovarian cancer is more common in white women than in African-American women. Women who are of Ashkenazi (Eastern European) Jewish descent have a higher risk of developing ovarian cancer in part due to a higher risk of BRCA abnormalities in this population.
Women are at high risk for ovarian cancer and for harboring a genetic mutation such as BRCA if they have a:
- First-degree relative (mother, sister, or daughter) with ovarian cancer at any age. The risk increases with the number of affected first-degree relatives.
- First-degree relative or two second-degree relatives (aunts or grandmothers) on the same side who had breast cancer before age 50 years.
- Family member with both breast and ovarian cancer.
- Family history of male breast cancer.
- Family history of hereditary non-polyposis colorectal cancer known as Lynch syndrome.
When a woman describes her family history to her doctor, she should include the history of cancer in women on both the mother's and the father's side. Both are significant.
Inherited mutations in the genes called BRCA1 and BRCA2 greatly increase the risk for ovarian and breast cancers. While these mutations are more common among women of Ashkenazi Jewish ancestry, they can occur in women of any ethnicity.
Women with a BRCA1 mutation have about a 44% lifetime risk for ovarian cancer. Women with a BRCA2 mutation have about a 17% lifetime risk for ovarian cancer. (By contrast, the lifetime ovarian cancer risk for women in the general public is about 1 in 55 or 1.3%.) These gene mutations are also associated with increased risks for breast cancer, fallopian tube cancer, pancreatic cancer, and prostate cancer in the male. In addition to an increased lifetime risk, women with these gene mutations tend to develop these cancers at an earlier age than that seen in the usual population of women with ovarian cancer.
Other genetic factors are also associated with increased risk. Women who have genetic mutations associated with hereditary non-polyposis colorectal cancer (HNPCC or Lynch syndrome) have about a 10% to 15% lifetime risk of developing ovarian cancer.
Personal Medical History
Women who have been diagnosed with breast cancer are at increased risk for ovarian cancer, even if they do not have BRCA mutations. Endometriosis, a condition in which the cells that line the cavity of the uterus grow in other areas of the body such as on the ovaries or on the other pelvic structures, increases the risk for ovarian cancer.
Women are at increased risk for ovarian cancer if they began menstruating at an early age (before age 12), have not had any children, had their first child after age 35, or experienced early menopause (before age 50).
There are also preventive factors associated with reproductive history. The more times a woman gives birth, the less likely she is to develop ovarian cancer. Breast-feeding for a year or more after giving birth may also decrease ovarian cancer risk.
Tubal ligation, a method of sterilization that ties off the fallopian tubes, is associated with a decreased risk for ovarian cancer. Similarly, hysterectomy, the surgical removal of the uterus, may decrease risk.
Women who use hormone therapy (HT) after menopause for longer than 5 years may have an increased risk for ovarian cancer. The risk seems to be particularly significant for women who take estrogen-only HT. The risk is less clear for combination estrogen-progestin HT.
Oral contraceptives (birth control pills) significantly reduce the risk of ovarian cancer, in some series by as much as 50%. The longer a woman takes oral contraceptives the greater the protection and the longer protection lasts after stopping oral contraceptives.
Women who are obese have an increased risk for ovarian cancer.
Preventive Strategies for Women at High Risk
Women with a strong family history of ovarian or related cancers should discuss preventive strategies with their providers.
Screening for BRCA Genetic Mutations
Guidelines from the U.S. Preventive Services Task Force (USPSTF) recommend BRCA screening for women at high risk for ovarian cancer due to personal or family history. The USPSTF does not recommend routine genetic screening or testing in women whose family history does not suggest BRCA mutations. Having several first-degree or second-degree relatives who have had breast, ovarian, fallopian tube, or peritoneal cancers is an indication of risk. Having a male family member with breast cancer is also an indication of risk.
Your provider can screen you using a questionnaire that evaluates your family and personal medical history, and other factors. If your provider decides you are at risk, you may be referred to a genetic counselor who can review your history and discuss with you whether you should be tested for the BRCA1 and BRCA2 mutations, or for other genetic mutations that may be present and are also associated with increased risks.
The genetic test uses DNA from a blood or saliva sample to check for these mutations. A positive test means that the mutations are present. It does not, however, mean that a woman will definitely develop ovarian or breast cancer. A negative test does not mean that a woman will never get ovarian cancer.
Removal of Ovaries (Oophorectomy)
Surgical removal of the ovaries called oophorectomy, significantly reduces the risk for ovarian cancer. When it is used to prevent cancer, the procedure is called a prophylactic oophorectomy.
Prophylactic oophorectomy is approximately 85% to 95% protective against ovarian cancer and is recommended for women at high risk for ovarian cancer. These women generally have the BRCA1 or BRCA2 genetic mutation, or have two or more first-degree relatives who have had ovarian cancer.
Bilateral oophorectomy is the removal of both ovaries. Bilateral salpingo-oophorectomy is the removal of both fallopian tubes plus both ovaries. Evidence is accumulating that many ovarian cancers actually arise in the fallopian tubes and secondarily involve the ovary. There is strong evidence that salpingo-oophorectomy is very effective in reducing risk for ovarian cancer in women who carry the BRCA1 or BRCA2 mutation.
Primary peritoneal carcinoma, a rare cancer that develops in the peritoneum (the thin membrane that lines the inside of the abdomen and gives rise to the epithelial lining of the ovary), can still develop in women who have their ovaries and tubes removed. Some of these peritoneal cancers may actually come from small tumors that originated in the fallopian tubes. Some evidence suggests that preventive salpingo-oophorectomy may reduce the risk for peritoneal cancer and fallopian tube cancers, in addition to ovarian cancer.
Oophorectomy causes immediate menopause, which can raise health concerns for premenopausal women. You should discuss all the risks and benefits of prophylactic oophorectomy with your health care team, as well as the option for hormone therapy after surgery.