Ovarian cancer risk factors: genes, hormones and what lowers the risk

What ovarian cancer is

Ovarian cancer is a cancerous tumor that forms in the tissues of an ovary. The ovaries are a pair of female reproductive glands that make eggs and female hormones (MedlinePlus). Cancer of the fallopian tubes and primary peritoneal cancer (in the tissue lining the belly) are closely related, and some experts count them as ovarian cancer (MedlinePlus). Cancer sometimes begins at the end of the fallopian tube near the ovary and spreads to the ovary (NCI PDQ).

Ovarian cancer is rare, but in the United States it is the sixth-leading cause of death from cancer in women and the leading cause of death from cancer of the female reproductive system (NCI PDQ). It is most common after menopause (NCI PDQ). A risk factor is anything that raises your chance of getting a disease; a protective factor lowers it (NCI PDQ). Avoiding risk factors and adding protective factors may lower your risk, but it does not mean you will not get cancer (NCI PDQ).

Risk factors that raise the risk

NCI lists these risk factors for ovarian, fallopian tube and primary peritoneal cancers (NCI PDQ):

• Family history. A woman whose mother or sister had ovarian cancer has a higher risk. So does a woman with two or more relatives with ovarian cancer (NCI PDQ). MedlinePlus also names an aunt or grandmother (MedlinePlus).
• Inherited gene changes. Changes in genes such as BRCA1 or BRCA2 raise the risk (NCI PDQ). These changes also raise the risk of breast and other cancers (MedlinePlus).
• Inherited syndromes. Familial site-specific ovarian cancer syndrome, familial breast/ovarian cancer syndrome, and hereditary nonpolyposis colorectal cancer (HNPCC, also called Lynch syndrome) (NCI PDQ).
• Menopause hormone therapy. Women taking hormone replacement therapy (HRT) after menopause have a slightly higher risk, and so do women who used it recently, even for less than 5 years. The risk is the same for estrogen only and for estrogen plus progestin. HRT through the skin may carry a lower risk than HRT by mouth, and the risk goes down over time after HRT is stopped (NCI PDQ).
• Weight and height. Excess body weight or obesity is linked to a higher risk of getting ovarian cancer and of dying from it. Being tall may be linked to a slightly higher risk (NCI PDQ).
• Endometriosis (NCI PDQ).
• Age. Being older, especially after menopause (MedlinePlus).
• Never having been pregnant (MedlinePlus).

Most ovarian cancers are caused by gene changes that happen during a person's lifetime; only some are inherited (MedlinePlus).

What is linked to a lower risk

NCI lists these protective factors (NCI PDQ):

• Birth control pills. Taking oral contraceptives lowers the risk, the longer the use the lower the risk may be, and the lower risk may last up to 30 years after stopping. The pill raises the risk of blood clots, more so in women who smoke (NCI PDQ).
• Giving birth. Women who have given birth have a lower risk than women who have not, and giving birth to more than one child lowers it further (NCI PDQ).
• Breastfeeding. The longer a woman breastfeeds, the lower her risk. Breastfeeding for at least 8 to 10 months gives the greatest drop (NCI PDQ).
• Tubal ligation (surgery to close both fallopian tubes) (NCI PDQ).
• Salpingectomy (removing one or both fallopian tubes). Some studies link it to a lower risk, and removing both tubes lowers the risk more than removing one (NCI PDQ).

None of these are reasons on their own to take a medicine or have surgery. Each has its own risks and benefits to talk through with your doctor.

Which ones you can change

For women at high risk

Women with an inherited BRCA1 or BRCA2 change or an inherited syndrome may choose risk-reducing salpingo-oophorectomy: surgery to remove the fallopian tubes and ovaries when there are no signs of cancer. NCI says it is very important to have a cancer risk assessment and counseling first. The surgery causes infertility and early menopause, and a small, rare risk of cancer in the peritoneum remains afterward (NCI PDQ).

The US Preventive Services Task Force recommends that women with a personal or family history of breast, ovarian, tubal or peritoneal cancer, or an ancestry linked to BRCA1/2 changes, be checked with a brief family risk tool, and get genetic counseling if it is positive (USPSTF 2019). The BRCA family history check walks through it.

Things that are not clearly linked

NCI says it is not clear whether these affect the risk (NCI PDQ):

• Diet. Studies have not found a strong link.
• Alcohol. Studies have not shown a link with ovarian cancer.
• Aspirin and NSAIDs. Some studies found a lower risk and others did not.
• Talc. Studies of talcum powder dusted on the perineum have not found clear evidence of a higher risk.
• Fertility drugs. Overall, no clear evidence of a higher risk, though the risk of invasive ovarian cancer may be higher in women who do not get pregnant after taking them.

Symptoms to report

Early ovarian cancer may not cause any symptoms, and by the time symptoms appear the cancer is often advanced (NCI PDQ) (MedlinePlus). MedlinePlus lists these signs (MedlinePlus):

• Pain, swelling, or a feeling of pressure in the belly or pelvis
• A sudden or frequent urge to urinate
• Trouble eating or feeling full
• A lump in the pelvic area
• Gas, bloating or constipation

Symptoms like these are common in healthy women too, which is one reason they are hard to use for early detection (USPSTF 2018). Talk to your doctor about symptoms that are new or do not go away.

Why there is no screening test for average risk

Pelvic exams, transvaginal ultrasound and the CA-125 blood test have all been studied. None of them, and not CA-125 and ultrasound together, has been shown to lower deaths from ovarian cancer (NCI PDQ). Screening can also give false-negative results that delay care, and false-positive results that lead to more tests, surgery and sometimes removal of an ovary that was not needed (NCI PDQ).

For these reasons the US Preventive Services Task Force recommends against screening for ovarian cancer in women without symptoms who are not known to have a high-risk hereditary cancer syndrome (grade D) (USPSTF 2018). The ovarian cancer screening check shows what it says for you, and screening tests by age lists the checks that are recommended.

Common questions

Is ovarian cancer linked to breast cancer?

Yes, through some of the same inherited gene changes. BRCA1 and BRCA2 changes raise the risk of both (MedlinePlus). See breast cancer risk factors.

Can a CA-125 test tell me I do not have ovarian cancer?

No. A raised CA-125 can come from ovarian cancer or other conditions, and screening results can look normal even when cancer is present (NCI PDQ).

Does having a risk factor mean I will get ovarian cancer?

No. Avoiding risk factors and adding protective factors may lower your risk, but neither one decides it (NCI PDQ). Talk to your doctor if you think you may be at risk (NCI PDQ).