Ovarian cancer

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Risk factors for ovarian cancer

A risk factor is something that increases the risk of developing cancer. It could be a behaviour, substance or condition. Most cancers are the result of many risk factors. A family history of the disease is the most important risk factor for developing ovarian cancer.

Epithelial ovarian carcinoma is the most common type of ovarian cancer. The number of new cases of this cancer (called the incidence) increases with age. Most epithelial ovarian carcinomas are found in women who have gone through menopause.

Some women can have a higher than average risk for ovarian cancer. Talk to your doctor about your risk. If you are at higher than average risk, you may need a personal plan for testing.

The following are risk factors for epithelial ovarian carcinoma. The risk factors for less common types of ovarian cancer are not well known and may not be the same as for epithelial ovarian carcinoma. But epithelial ovarian carcinoma and fallopian tube cancer share many of the same risk factors. Some experts think that this may be because some epithelial ovarian carcinomas can begin in a fallopian tube.

Risk factors are generally listed in order from most to least important. But in most cases, it is impossible to rank them with absolute certainty.

Research shows that there is no link between alcohol or coffee and a higher risk for epithelial ovarian carcinoma.

Known risk factors

There is convincing evidence that the following factors increase your risk for epithelial ovarian carcinoma.

Family history of ovarian cancer

A family history of ovarian cancer means that 1 or more close blood relatives have or had ovarian cancer. Sometimes ovarian cancer develops in a family more often than would be expected by chance. It may not be clear if the family’s pattern of cancer is due to chance, shared lifestyle factors, a genetic risk passed from parents to children or a combination of these factors.

If several of your relatives have ovarian cancer, you can have a higher risk of developing the disease. These relatives can be on either your mother’s or your father’s side of the family.

You can have a higher risk of developing ovarian cancer if you have 1 first-degree relative (mother, sister or daughter) with the disease. The risk of developing ovarian cancer is greater if your mother had the disease than if your daughter had it. Your risk can be even higher if your relative was diagnosed with ovarian cancer before they were 50 years of age or before they went into menopause.

Having 2 or more first-degree relatives with ovarian cancer can also increase your risk for the disease.

You can have a slightly higher risk for ovarian cancer if you have 1 first-degree relative and 1 second-degree relative (aunt, grandmother or niece) with the disease.

BRCA gene mutations

Breast cancer gene 1 (BRCA1) and breast cancer gene 2 (BRCA2) normally help control the growth of cancer cells. Mutations in these genes (which can be inherited from either parent) increase the risk for breast cancer. These mutations also increase the risk for ovarian cancer. But not all women with mutations in the BRCA1 or BRCA2 gene will develop ovarian cancer.

Overall, the BRCA1 mutation increases the risk for ovarian cancer more than the BRCA2 mutation. Women with the BRCA1 mutation are more likely to develop ovarian cancer before they are 50 years of age. Women with the BRCA2 mutation are more likely to develop the disease after they are 60 years of age. Ovarian cancer is usually diagnosed at a younger age in women who do not have a BRCA gene mutation.

Ovarian cancer is likely linked to an inherited BRCA1 or BRCA2 gene mutation if the woman has:

  • several family members with breast or ovarian cancer
  • 1 or more female relatives who developed breast cancer before they were 50 years of age
  • a relative with both breast and ovarian cancer
  • family members who develop cancer in both breasts (called bilateral breast cancer)
  • a male relative with breast cancer
  • Ashkenazi (Eastern European) Jewish ancestry

Serous carcinoma (which is a type of epithelial ovarian carcinoma) is more commonly linked to BRCA gene mutations than other types of ovarian cancer. Having ovarian cancer linked to a BRCA gene mutation also increases the risk of developing papillary serous carcinoma of the peritoneum, which is a cancer in the lining of the abdominal cavity.

Women with ovarian cancer related to a BRCA gene mutation also have a higher than average risk of developing breast and other cancers. Talk to your doctor about your risks. Genetic risk assessment and genetic testing may be an option for some women.

Lynch syndrome

Lynch syndrome is also called hereditary non-polyposis colorectal cancer (HNPCC). It is an uncommon genetic condition that increases the risk for colorectal and other cancers, including ovarian cancer. Women with type B Lynch syndrome, or Lynch II, have a higher risk of developing epithelial ovarian carcinoma in their lifetime.

Never being pregnant or giving birth

Women who have never been pregnant have a higher risk of developing ovarian cancer than women who have been pregnant. Researchers think that the lower risk may be because the hormones that are present during pregnancy have a protective effect. It is possible that the higher risk in women who have never been pregnant is linked to the factors that may make it difficult for her to become pregnant.

The risk for ovarian cancer is also higher in women who have never given birth, even if they have been pregnant. Researchers are not sure if this greater risk is related to the same factors that increase the risk for ovarian cancer in women who have never been pregnant.

Family history of certain cancers

Women who have a family history of breast cancer have a higher risk of developing ovarian cancer. A family history of colorectal, uterine or pancreatic cancer may also increase the risk for ovarian cancer.

Personal history of breast cancer

Women who have been diagnosed with breast cancer have a higher risk of developing ovarian cancer. This could be because of a BRCA gene mutation. Some of the same risk factors for breast cancer that are related to a woman’s menstruation history may also increase her risk of developing ovarian cancer. These risk factors include starting your period early (younger than 11 years of age) or starting menopause later (after age 55).

Tall adult height

Tall women have a slightly higher risk for ovarian cancer. Researchers think this increased risk may be due to developmental factors such as growth and puberty hormones.

Ashkenazi Jewish ancestry

Women of Ashkenazi (Eastern European) Jewish ancestry are more likely than women in the general population to carry a BRCA1 and BRCA2 gene mutation. About 1 in 40 Ashkenazi Jewish women carry a BRCA gene mutation, which is considerably higher than in the general population. Women with these mutations have a higher chance of developing ovarian cancer.

Hormone replacement therapy

Hormonal replacement therapy (HRT) is used to manage the symptoms of menopause (such as hot flashes, vaginal dryness and mood swings).

Research suggests that HRT with estrogen alone, as well as combined HRT with both estrogen and progesterone, increases the risk for ovarian cancer. The longer you take estrogen, the greater your risk for the disease. Women who have taken HRT for more than 5 years have a greater risk than women who have taken it for less than 5 years. One recent large study also found that how recently a woman has taken HRT affects her risk. Current users of HRT have a higher risk compared to women who have stopped taking HRT, no matter how long they took it.

Smoking

Smoking increases a woman’s risk of developing mucinous carcinoma (a type of epithelial ovarian carcinoma).

Asbestos

Women exposed to asbestos, especially in the workplace, have a higher risk of developing ovarian cancer.

Endometriosis

The endometrium is the lining of the uterus. Endometriosis occurs when the endometrium grows outside of the uterus. It can grow on the ovaries, behind the uterus, on the small intestine, on the large intestine or on the bladder. Women with endometriosis may have a higher risk of developing ovarian cancer, especially if the endometriosis involves the ovaries. Other studies show that the risk for certain types of ovarian cancer, including clear cell and endometrioid tumours, may be higher in women with endometriosis.

Possible risk factors

The following factors have been linked with ovarian cancer, but there is not enough evidence to show they are known risk factors. More research is needed to clarify the role of these factors for ovarian cancer.

Being obese

Being obese means having a body mass index (BMI) of 30 or more. Some studies have shown that being obese may increase the risk of developing ovarian cancer.

Using talc on the genitals

Research studies on the use of talc on the genital area and the risk of ovarian cancer have mixed results. Some research suggests that in the past certain sources of talcum powder may have been contaminated with asbestos or may have contained asbestiform fibres, which are fibres that have similar properties as asbestos. Talcum powder available today is tested to ensure that it does not contain asbestos. Talcum powders made with cornstarch do not increase the risk for ovarian cancer.

Unknown risk factors

It isn’t known whether or not the following factors are linked with ovarian cancer. It may be that researchers can’t show a definite link or that studies have had different results. More research is needed to see if the following are risk factors for ovarian cancer:

  • eating certain amounts or types of foods, such as milk and milk products, fat, vegetables, fruit or meat
  • using fertility drugs
  • sedentary behaviour, which means sitting too much

Questions to ask your healthcare team

To make the decisions that are right for you, ask your healthcare team questions about risks.

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