What Causes Ovarian Cancer?

Ovarian cancer happens when abnormal cells grow uncontrollably in and around the ovaries. The cells multiply rapidly and form a tumor, which can invade and destroy healthy tissues. The exact cause of ovarian cancer is not fully understood. Certain factors—including genetic, environmental, lifestyle, and hormonal—are known to increase the risk of developing ovarian cancer.

Having one or more risk factors does not necessarily mean that you will develop ovarian cancer. On the other hand, some people with no known risk factors develop it anyway. This article explores what we know about ovarian cancer causes, and risk factors that may increase the likelihood of developing it. 

What Causes Ovarian Cancer? 

Ovarian cancer begins when cells in the ovary, fallopian tube, or nearby structures develop changes (mutations) in their DNA. These changes can cause the abnormal cells to grow out of control, eventually forming a mass (tumor). The cancer cells can spread (metastasize) through the abdomen, pelvis, lymph nodes, and to more distant areas of the body. 

Theories 

Researchers aren’t sure what causes the mutations that lead to ovarian cancer. There are a number of theories about why it develops, based on what we know about risk factors and protective factors. 

Hormone Replacement Therapy 

Hormone replacement therapy (HRT)—used to manage symptoms of menopause like sweating and hot flashes—may increase the risk of developing ovarian cancer. Both estrogen-only and combined estrogen/progesterone HRT have been linked to an increased risk. The risk is highest for those who are currently taking hormones and decreases over time after the HRT is stopped. 

Late Onset Menopause 

Menopause is characterized by not having a period for 12 consecutive months and marks the permanent end of your menstrual cycle. Menopause that starts after the age of 55 (the average age is 51) is linked to a greater risk of ovarian cancer. This may be due to prolonged exposure to estrogen, which is at its highest during your childbearing years. Research suggests that a higher number of ovulatory cycles may lead to ovarian cancer because ovulation is associated with inflammation, which is known to cause cancer. 

Endometriosis 

Endometriosis is a condition where the tissue lining the uterus (the endometrium) grows outside the uterus. People with endometriosis have a 1.7 times higher likelihood of developing ovarian cancer than those without. High estrogen levels, gene mutations, and inflammation associated with endometriosis may play a role in this correlation.

Reproductive History 

The risk of ovarian cancer is higher for those who have never given birth. A first full-term pregnancy before the age of 26, multiple pregnancies, and breastfeeding are associated with a decreased risk. The specific reason for this remains unclear, but it may be that pregnancy hormones—or the break from ovulation that pregnancy and breastfeeding offer—have protective effects against ovarian cancer. 

Weight 

A body mass index (BMI) of 30 or higher is associated with a slightly higher risk of ovarian cancer, especially in those who have never used hormone replacement therapy (HRT). Excess amounts of estrogen produced by fat tissue may contribute to the increased risk. Chronic inflammation, which is linked to obesity, may also play a role. 

Is Ovarian Cancer Hereditary? 

Ovarian cancer can be hereditary (passed down from parent to child). About 25% of ovarian cancers are linked to inherited gene mutations. Having a close relative (mom, sister, daughter) with a history of ovarian cancer increases a person’s risk of developing the disease. 

There are many hereditary gene mutations that are connected to ovarian cancer development. The most well-known genetic mutations associated with the development of ovarian cancer are in the BRCA1 and BRCA2 genes. An estimated 10% of all ovarian cancer diagnoses are linked to mutations in these genes, which also increase the risk of breast cancer. The risk of ovarian cancer increases with age if you carry BRCA gene mutations, but not everyone with these genetic mutations will develop the disease.

Lynch syndrome, or hereditary nonpolyposis colorectal cancer (HNPCC), is an inherited disorder that increases the risk of many types of cancers, particularly colorectal cancer, endometrial cancer, and ovarian cancer. Mutations in the genes of MLH1, MSH2, MSH6, PMS2, and EPCAM have been linked to Lynch syndrome. Up to 1 in 300 people may carry a genetic mutation associated with Lynch syndrome. The lifetime risk of ovarian cancer in those with Lynch syndrome is an estimated 8%. 

If you have a family history of ovarian, breast, and/or colon cancer and want to learn more about your own hereditary risk, talk to your healthcare provider about genetic testing. 

Who Gets Ovarian Cancer? 

Some people are more likely to develop ovarian cancer than others: 

• Age: Ovarian cancer is most common after menopause, and half of all ovarian cancers are diagnosed in people ages 63 or older. 
• Sex: An estimated 1 in 78 people with ovaries will develop ovarian cancer in their lifetime. 
• Ethnicity: Ovarian cancer is more common in white women than in Hispanic, Black, and Asian women. An estimated 1 in 40 Ashkenazi Jewish people carry a BRCA gene mutation, which increases the risk of developing ovarian cancer at a young age. 

Risk Factors 

In addition to genetics, age, and reproductive history, several other factors may play a role in the development of ovarian cancer. Some of these factors are out of your control, and others, like lifestyle habits, can be changed to lower your risk. These include:

• Medical history: A personal or family history of breast, colon, or ovarian cancer raises your risk of ovarian cancer.
• Smoking: Smoking is linked to an increased risk of multiple types of ovarian cancer. 
• Diet: Eating a diet high in animal fats (e.g., red meats) and dairy products is linked to a higher risk for ovarian cancer. Research shows that eating a low-fat diet after menopause can lower the risk. 
• Body weight: Being overweight or obese is associated with an increased risk of ovarian cancer. 
• Infertility: Infertility is linked to an increased risk of ovarian cancer. Previous use of fertility drugs such as Clomid (clomiphene citrate) and in vitro fertilization (IVF) may also elevate the risk of developing the disease.
• Talcum powder use: Applying talcum powder (talc) to the genital area or to sanitary pads may slightly elevate the risk of ovarian cancer. This is not well-established and more research is needed. 

A Quick Review 

Ovarian cancer occurs when abnormal cells in the ovaries and/or supporting structures grow and divide rapidly, eventually forming a tumor. The exact cause of ovarian cancer is unknown, but research suggests that genetic, lifestyle, and hormonal factors may play a role.

If you have a family history of ovarian, breast, and/or colorectal cancers, talk to your healthcare provider about your personal risk of developing ovarian cancer. They can discuss your risk factors and may recommend genetic testing and certain preventive measures to help lower your risk.