Ovarian cancer and breast cancer share some risk factors. This means that some people have a higher risk of developing both types of cancer. In some cases, these risk factors can be controlled, allowing a person with ovarian cancer to lower their chances of developing breast cancer. People who have a very high risk of breast cancer may also be able to use medication, surgery, and screening tests to reduce the risk or catch cancer early.

Causes and Risk Factors

Understanding what causes cancer can shed light on why a person may develop different kinds of cancer. Cancer forms when genes undergo changes and cause a cell to start behaving abnormally and grow out of control. These gene changes may be inherited (passed down from parent to child), or they may happen as a result of environmental or lifestyle changes. Sometimes, genetic, environmental, or lifestyle factors can increase the risk of more than one type of cancer.

Inherited Genetic Changes in Breast and Ovarian Cancer

Breast and ovarian cancer can both be caused by some of the same inherited gene mutations. Many of these cancers are caused by changes in the BRCA1 or BRCA2 genes. In normal cells, these genes allow the cell to fix damage, preventing them from turning cancerous. When cells have mutated BRCA genes, DNA damage cannot easily be fixed, so they are more likely to start growing abnormally.

Inherited gene changes are present at birth, and they can be found in every cell within the body. When a person has inherited BRCA mutations, doctors refer to the condition as hereditary breast and ovarian cancer syndrome.

Changes in BRCA1 or BRCA2 can increase the risk of both breast and ovarian cancers:

• About 1.6 percent of women without BRCA mutations develop ovarian cancer at some point in their lives.
• Women with BRCA1 mutations have a 40 percent to 60 percent chance of being diagnosed with ovarian cancer. Those with BRCA2 mutations have a 20 percent to 35 percent lifetime risk.
• Around 13 percent of women without BRCA mutations are diagnosed with breast cancer.
• BRCA1 mutations lead to a 55 percent to 72 percent risk of developing breast cancer. The lifetime risk for women with BRCA2 mutations is 45 percent to 69 percent.

BRCA mutations, and in particular mutations in BRCA1, are more likely to lead to triple-negative breast cancer. Triple-negative breast cancer is an aggressive type of breast cancer that often comes with a poor outlook.

BRCA gene changes also increase the risk of other cancers, including cancer of the fallopian tubes (the tubes that carry eggs from the ovaries to the uterus), peritoneal cancer (cancer in the lining of the inside of the abdomen), and pancreatic cancer. There may be an association with melanoma, an aggressive form of skin cancer. Men who inherit BRCA gene changes also have an increased risk of developing breast or prostate cancer.

People who have BRCA mutations are more likely to be diagnosed with both breast and ovarian cancers. When a woman has ovarian cancer caused by another factor besides BRCA gene changes, she may not have an increased risk of breast cancer.

Environmental and Lifestyle Factors

Most cancer-causing gene changes are not inherited. Instead, they happen throughout a person’s life. They may develop in one or more cells from exposure to substances that damage DNA like ultraviolet light or radiation. They may also develop randomly as a cell grows and divides. Some environmental and lifestyle factors can increase the chances that genes mutate and change. These factors make people more likely to be diagnosed with multiple types of cancer.

Factors that raise the risk of ovarian cancer or breast cancer include:

• Being older
• Being obese
• Never having had children
• Having one’s first child at a later age (older than 35 years old for ovarian cancer or older than 30 years old for breast cancer)
• Using hormone replacement therapy during or after menopause

If you have any of these shared risk factors, you are slightly more likely to develop ovarian cancer and breast cancer.

Screening and Lowering Risk

People with ovarian cancer who are concerned about their breast cancer risk should talk to their doctor to learn more about potential next steps. If you have a history of ovarian or breast cancer, you may be a candidate for genetic testing to determine whether you have any inherited gene changes. You may also be able to change certain habits in order to lower your risk of developing breast cancer in the future. Additionally, you should make sure to be screened for breast or other cancers based on your doctor’s recommendations.

Genetic Testing

Only 1 out of 10 people with ovarian cancer have inherited mutations in BRCA genes. This means that most people diagnosed with ovarian cancer don’t have a gene change that puts them at risk for breast cancer. However, certain signs indicate that a case of ovarian cancer may be caused by an inherited gene change.

Inherited BRCA mutations usually cause multiple cases of cancer within the same family. If you are diagnosed with ovarian cancer, your doctor will likely ask you whether you have a family history of ovarian or other cancers. Additionally, there are other signs that a case of ovarian cancer may have been caused by a BRCA mutation. You may be at risk if you or anyone in your family:

• Had breast cancer before the age of 50
• Were diagnosed with triple-negative breast cancer at a young age
• Developed breast cancer in both breasts
• Have a male relative with breast cancer
• Had pancreatic cancer

If your doctor thinks that you may have a genetic mutation that leads to a higher risk of cancer, they may recommend genetic counseling and genetic testing. In this case, you will meet with a genetic counselor to talk about your cancer risk, and you may undergo tests that help determine whether you have certain gene changes. These tests are very simple and involve either a blood or saliva test. When one person within a family finds out that they have an inherited gene change, other family members should be informed and may also want to be tested to determine their risk levels.

Lowering Your Risk Using Lifestyle Changes

For most people, ovarian cancer is not caused by inherited gene changes, and genetic testing is not helpful. However, there may be things you can do to lower your risk of developing breast cancer. Some risk factors, such as growing older, can’t be changed. You can have more influence over other factors. Strategies to reduce breast cancer risk include:

• Stop drinking alcohol, or have no more than one drink per day
• Get more physical activity (30 to 60 minutes of exercise at least five days per week)
• Maintain a healthy weight
• Eat more vegetables, fruit, and dairy
• Avoid red meat or processed meat
• Don’t use hormone replacement therapy while going through menopause
• If you give birth, breastfeed for a few months or more

Women who have a high risk of developing breast cancer may choose to use more aggressive prevention strategies. Medications like Nolvadex (tamoxifen) are often used to treat breast cancer, but they may also help prevent it.

Women with BRCA mutations sometimes choose to talk to their doctor about surgical options to reduce risk. During a prophylactic mastectomy, a person’s breast tissue is removed. Another possible procedure is an oophorectomy (removal of the ovaries). This surgery reduces levels of the estrogen hormone in the body, which can decrease the chances of developing breast cancer.

All of these preventive options come with side effects. Talk to your doctor to weigh the risks and benefits of each therapy.

Breast Cancer Screening

Having regular screenings can help people find breast cancer early, which may lead to better outcomes. Doctors screen for breast cancer using mammograms — imaging tests that use X-rays to get a clearer picture of the inside of the breast.

The American Cancer Society recommends that women who have an average risk of breast cancer start getting mammograms in their 40s. Women should have yearly mammograms when they are between 45 and 54 years old. Starting at age 55, women should get a mammogram every one to two years.

Women who have a high risk of breast cancer should get mammograms earlier and more often. Those considered to be at high risk include women who have a family history of breast cancer, have a BRCA mutation, or have had radiation therapy to the chest. The American Cancer Society suggests that high-risk women start getting yearly mammograms when they turn 30 years old. In addition to mammograms, women with a higher risk may also need to undergo a breast MRI, which creates a more detailed picture of the breast.

Talk With Others Who Understand

MyOvarianCancerTeam is the social network for people with ovarian cancer and their loved ones. More than 3,000 members come together to ask questions, give advice, and share their stories with others who understand life with ovarian cancer.

Are you living with ovarian cancer or breast cancer? Share your experiences in the comments below, or start a conversation by posting on MyOvarianCancerTeam.