Ovarian Cancer: Causes, Risk Factors, and Prevention

One of the biggest goals of ovarian cancer research is to better understand what causes this relatively rare but extremely life-threatening disease.

Scientists have identified certain factors that raise a woman’s risk of developing the most common form of ovarian cancer, epithelial ovarian cancer.

Yet only a small percentage of women with these risk factors will develop the disease. Most won’t — and researchers are still working to understand exactly why.

Clinical studies based on this finding are investigating new prevention, early detection, and treatment strategies. (2)

Ovarian Cancer Risk Factors: What You Can and Can’t Control

Women may be able to lower their risk in some ways but not others. Researchers have identified the following risk factors for epithelial ovarian cancer:

• Age The older you get, the higher your risk. Most ovarian cancers develop after menopause.
• Being overweight or obese Researchers have found a link between overweight and ovarian cancer, though not necessarily the most life-threatening types.
• Pregnancy after 35 Having children after age 35 or never carrying a child to term raises risk.
• Using fertility treatment Some studies suggest a connection between IVF (in vitro fertilization) treatment and so-called “borderline” ovarian tumors, though there has been conflicting evidence.
• Hormone therapy This includes having hormone therapy after menopause, especially estrogen alone (without progesterone) for many years.
• Family history Having a family history of ovarian, breast, or colorectal cancer increases your risk.
• Having a family cancer syndrome This accounts for 5 to 10 percent of ovarian cancers and is caused by inherited changes (mutations) in certain genes, such as BRCA1 and BRCA2.
• Having had breast cancer The inherited mutations that raise cancer risk do so for both breast and ovarian cancers.
• Smoking This hasn’t been shown to raise overall ovarian cancer risk but has been linked to an increase in an uncommon type of epithelial ovarian cancer tumor called a mucinous carcinoma. (3)

Factors That Can Lower Ovarian Cancer Risk

Researchers have identified two factors that make a woman less likely to develop ovarian cancer:

• Pregnancy and breastfeeding Women who became pregnant before age 26 and carry to term are at lower risk, with each subsequent full-term pregnancy diminishing the risk further. Breastfeeding is protective, too.
• Birth control Women who have used oral contraceptives are at lower risk. So are women who’ve had a tubal ligation (had their fallopian tubes tied) or used an IUD (intrauterine device) for a short time. Women who’ve had a hysterectomy (removal of the uterus) see their ovarian cancer risk drop by about one-third. (3)

Since both pregnancy and oral contraceptives decrease the number of times an ovary releases an egg, some researchers theorize that there may be a link between ovulation and ovarian-cancer risk.

What Role Does Genetics Play in Ovarian Cancer?

Scientists have focused an enormous amount of attention on identifying the DNA changes that cause normal, healthy cells to become malignant.

For ovarian cancer, particularly the epithelial kind, scientists point to mutations in the genes that control cell division and growth.

These changes may be inherited from one’s parents, acquired during one’s lifetime, or — most likely — both.

For the 5 to 10 percent of ovarian cancers related to family cancer syndromes, genetics play a key role. The most prevalent of these conditions, hereditary breast and ovarian cancer syndrome, is caused by mutations in the genes BRCA1 or BRCA2.

While women in the general population face an ovarian cancer lifetime risk of less than 2 percent, an estimated 44 percent of women with the BRCA1 mutation and about 17 percent of women with the BRCA2 mutation will develop ovarian cancer before age 80, according to the National Cancer Institute. (4)

For people of Ashkenazi (Eastern European) Jewish descent, BRCA1 and BRCA2 mutations are 10 times more common than in the general U.S. population. (3)

While 1 in 400 people in the United States have one of these mutations, 1 in 40 people with Ashkenazi Jewish heritage do. (5)

Finding Out if You Have a Dangerous Mutation

The American Cancer Society recommends that women consult with a genetic counselor if they believe they may be at high risk for ovarian cancer.

The counselor will review family and medical history to predict whether there may be a gene mutation that raises risk; discuss the pros and cons of testing; and help put any findings into context.

Then, if the patient wants to move forward, a DNA sample (usually blood or saliva) will be sent to a laboratory for testing. (6)

Women can also choose to take an at-home genetic test. In March 2018, the U.S. Food and Drug Administration approved the first such test for BRCA1 and BRC2 mutations, by the company 23andMe, which can be done without the involvement of a doctor of genetic counselor. (7)

Customers send a saliva sample to the company through the mail and receive results at home the same way.

The 23andMe test can detect 3 out of more than 1,000 known BRCA mutations — the three that are most common among people of Ashkenazi Jewish descent.

This means a negative result does not rule out the possibility that a person carries other BRCA mutations that increase cancer risk.

Should Women at Highest Risk Undergo Ovarian Cancer Screening?

Researchers have been studying the use of two screening methods to detect ovarian cancer early: transvaginal ultrasound (an imaging method that uses sound waves to look at the uterus, fallopian tubes, and ovaries) and a blood test that looks for elevated levels of the protein CA-125.

These screening tests have not been shown to reduce ovarian cancer–related deaths among women at average risk and can result in a substantial number of false positives and negatives. No major medical organization supports their use in the general population.

Still, some organizations do recommend these screening tests for women with inherited mutations, such as BRCA1 and BRCA2, that significantly raise ovarian cancer risk.

Memorial Sloan Kettering Cancer Center in New York City advises women with BRCA1 mutations to begin these screening tests between ages 30 and 35 and women with BRCA2 to begin between ages 35 and 40. (8)

Noting the limitations of these tests, Memorial Sloan Kettering recommends that women with BRCA1 and BRCA2 mutations consider reducing their risk by having their ovaries and fallopian tubes removed when childbearing is no longer a priority. (8)

Another option for women with BRCA mutations is to begin taking oral contraceptives, which studies have shown can reduce ovarian cancer risk.

But breast cancer risk goes up slightly with oral contraceptive use of over five years. (9)