Causes and Risk Factors
What causes ovarian cancer?
The causes of ovarian cancer are still unknown.
- Genetic changes that may occur during one’s life, known as acquired (somatic) gene mutations
- A person can be born with inherited gene mutations (hereditary gene mutations also known as germline mutations)
How can you reduce the risk of ovarian cancer?
Being pregnant and taking birth control pills can lower risk of ovarian cancer. Tubal ligation and hysterectomy are linked with a lower risk of ovarian cancer.
Additionally, based on research, it is believed that many if not almost all high-grade serous ovarian cancers (the most common subtype) previously thought to originate in the ovaries actually arise from precursor lesions that begin in the fallopian tubes. Consequently, removal of the fallopian tubes may reduce the risk of ovarian cancer. This is currently under study, but many providers recommend removal of the fallopian tubes for benign indications, in a procedure called opportunistic salpingectomy.
Ovarian Cancer Risk Factors
Research has shown that certain risk factors increase the likelihood of getting ovarian cancer. Other factors may actually decrease a woman’s probability of getting the disease. Not all people with risk factors will get ovarian cancer. Some women who get the disease have no known risk factors, and most women with risk factors will not get ovarian cancer. However, if you think you may be at risk for ovarian cancer, you should speak with your doctor.
Factors That May Increase Ovarian Cancer Risk
Genetics: BRCA1 and BRCA2
About 20 to 25 percent of women diagnosed with ovarian cancer have a hereditary tendency to develop the disease. The most significant risk factor for ovarian cancer is an inherited genetic mutation in one of two genes: breast cancer gene 1 (BRCA1) or breast cancer gene 2 (BRCA2). Inherited mutations in these genes are responsible for about 10 to 15 percent of all ovarian cancers.
Since these genes are linked to both breast and ovarian cancer, women who have had breast cancer may also have an increased risk of ovarian cancer.
Learn more about genetic counseling and testing.
Genetics: Lynch Syndrome
Another known genetic link to ovarian cancer is an inherited syndrome called hereditary nonpolyposis colorectal cancer (HNPCC or Lynch syndrome). Lynch syndrome elevates the risk of ovarian cancer via mutations in the MLH1, MSH2, and MSH6 genes. People with Lynch Syndrome have about a 12 percent lifetime risk of developing ovarian cancer and a 40-60 percent chance of developing uterine cancer.
Other Genetic Markers
Scientists are still discovering additional genetic mutations that are associated with elevated ovarian cancer risk. Studies have found that mutations in RAD51C, RAD51D, BRIP1, PALB2, STK11, and ATM are all linked to a higher than average risk of developing the disease.
Women with a grandmother, mother, daughter or sister with ovarian cancer but no known genetic mutation may still have an increased risk of developing ovarian cancer. The lifetime risk of a woman who has a first degree relative with ovarian cancer is five percent (the average woman’s lifetime risk is 1.4 percent).
While it accounts for only a limited number of cases, heredity is a strong risk factor for ovarian cancer. Family history should be considered; however, many women without a family history may still have a gene mutation associated with risk for ovarian cancer. All women diagnosed with ovarian cancer, primary peritoneal or fallopian tube cancer should be referred for genetic counseling and consideration of genetic testing.
Family history of any of the following cancers may indicate an increased risk: breast cancer, ovarian cancer, uterine cancer, colorectal cancer.
Personal history of cancer or endometriosis
Women who have had breast, uterine, or colorectal cancer have a higher risk of ovarian cancer. Having endometriosis increases the risk of clear cell and endometrioid ovarian cancers.
All women are at risk of developing ovarian cancer regardless of age; however ovarian cancer rates are highest in women aged 55-64 years. The median age at which women are diagnosed is 63, meaning that half of women are younger than 63 when diagnosed with ovarian cancer and half are older.
Reproductive History and Infertility
Research suggests a relationship between the number of menstrual cycles in a woman’s lifetime and her risk of developing ovarian cancer. A woman may be at an increased risk if she:
- started menstruating at an early age (before 12)
- has not given birth to any children
- had her first child after 30
- experienced menopause after 50
- has never taken oral contraceptives
- experienced infertility
Hormone Replacement Therapy
Doctors may prescribe hormone replacement therapy to alleviate symptoms associated with menopause (hot flashes, night sweats, sleeplessness, vaginal dryness) that occur as the body adjusts to decreased levels of estrogen. Hormone replacement therapy usually involves treatment with either estrogen alone (for women who have had a hysterectomy) or a combination of estrogen with progesterone or progestin (for women who have not had a hysterectomy).
Women who use hormone replacement therapy may be at an increased risk for ovarian cancer. Recent studies indicate that using a combination of estrogen and progestin for five or more years significantly increases the risk of ovarian cancer in women who have not had a hysterectomy. Ten or more years of estrogen use increases the risk of ovarian cancer in women who have had a hysterectomy.
Various studies have found a link between obesity and ovarian cancer. A 2009 study found that obesity was associated with an almost 80 percent higher risk of ovarian cancer in women 50 to 71 who had not taken hormones after menopause.
Reducing Ovarian Cancer Risk
Women can reduce the risk of developing ovarian cancer in many ways, and in some cases there may even be ways to prevent ovarian cancer in its most common form, by surgically removing the fallopian tubes and ovaries. However, there is no established prevention method proven to prevent all forms of ovarian cancer.
All women are at risk because ovarian cancer does not strike only one ethnic or age group. A health care professional can help a woman identify ways to reduce her risk as well as decide if consultation with a genetic counselor is appropriate.
Oral Contraceptive Use
The use of oral contraceptives (birth control pills) decreases the risk of developing ovarian cancer, especially when used for several years. Women who use oral contraceptives for five or more years have about a 50 percent lower risk of developing ovarian cancer than women who have never used oral contraceptives. This is also true for women at high risk as a result of BRCA gene mutations.
Pregnancy and Breastfeeding
Pregnancy and breastfeeding are linked with a reduced risk of ovarian cancer, likely because women ovulate less frequently when pregnant or breastfeeding. Multiple pregnancies or having first full-term pregnancy before the age of 26 decreases risk.
Studies now suggest that a bilateral salpingectomy — surgical removal of both fallopian tubes — may prevent many cases of the most common ovarian cancer subtype, high-grade serous carcinoma. A bilateral salpingectomy leaves the ovaries in-tact, which means patients who undergo the procedure do not immediately enter menopause. For those who wish to have children, a bilateral salpingectomy can preserve fertility by leaving open the option for in-vitro fertilization.
Removal of the fallopian tubes may be performed at the same time as other routine gynecologic surgeries such as a hysterectomy, even in people without a family history of cancer. Removal of the fallopian tubes at the time of another pelvic surgery is referred to as an opportunistic salpingectomy. Though research is ongoing, opportunistic salpingectomies are becoming more common as doctors have recognized their potential for ovarian cancer prevention, even for those at average risk. In early 2023, the Society of Gynecologic Oncology (SGO) endorsed OCRA’s statement about preventing many cases of ovarian cancer by removing the fallopian tubes
Removal of the Ovaries and Fallopian Tubes
Women can also greatly reduce their risk of ovarian cancer by having their ovaries and fallopian tubes removed, in a surgical procedure known as prophylactic bilateral salpingooophorectomy. Primary peritoneal cancer, which is microscopically almost identical to ovarian cancer, can still occur after this procedure, but is infrequent. One recent study suggests that women with BRCA1 mutations gain the most benefit by removing their ovaries before age 35.
For those with a known genetic predisposition to developing ovarian cancer, removal of the ovaries and fallopian tubes is worth considering. However, there are risks associated with removing the ovaries and fallopian tubes; women should speak to their doctors about whether this procedure is appropriate for them.
Having a hysterectomy, or removal of the uterus while leaving the ovaries, may decrease the risk of ovarian cancer by 33 percent, according to the American Cancer Society. Having fallopian tubes tied (tubal ligation) may reduce risk by up to 67 percent, the American Cancer Society says, though researchers aren’t sure why this is the case.