Your genes are passed down to you from your parents. At the moment of conception, you inherit half of your genes from your mother and the other half from your father.

You inherit genes that determine your hair, eye, and skin color, but you can also inherit genes that lead to unfavorable outcomes. In some cases, parents pass along genes for diseases, such as breast cancer.

Although inherited genes can cause breast cancer, they aren’t always the cause. In fact, only 5 to 10 percent of breast cancers are related to inherited genes. Breast cancer can also be caused by gene mutations that are not inherited. If this type of mutation occurs in a gene called HER2, it may result in HER2-positive breast cancer.

Human epidermal growth factor receptor 2 (HER2) is a gene that creates HER2 proteins. HER2 proteins act as receptors on breast cells and promote breast cell growth. Everyone has HER2 in their breast cells.

In a healthy breast cell, HER2 is responsible for repairing the cell and growing more cells. If the HER2 gene mutates, it causes an uncontrolled increase in HER2 protein. This causes cells to grow and divide out of control, which may lead to cancer. In about 20 percent of breast cancer cases, HER2 genes don’t function correctly.

HER2-positive breast cancer is not inherited from a parent. Instead, it’s considered a somatic genetic mutation. Somatic gene mutations occur after conception. Having a close relative with HER2-positive breast cancer does not increase your risk for breast cancer or HER2-positive breast cancer.

Learn more: HER2-positive breast cancer survival rates and other statistics »

HER2-positive breast cancers are sometimes more aggressive than other types of breast cancer. Additionally, HER2-positive breast cancers don’t always respond to hormone treatment.

If you’ve been diagnosed with breast cancer, your doctor may conduct a test to determine if your breast cancer is HER2-positive. If so, this will affect your treatment course.

HER2 testing are sometimes wrong, however. If your breast cancer is HER2-positive, but your test results incorrectly show it’s negative, this may greatly impact your cancer treatment. Talk with your doctor about their confidence in your test results. If you’re concerned, or if your results are borderline, ask for a second HER2 test.

Most inherited breast cancer cases can be traced to one of two abnormal genes: breast cancer gene one (BRCA1) and breast cancer gene two (BRCA2).

Everyone has both BRCA1 and BRCA2 genes. They’re designed to repair cell damage and help restore normal, healthy breast cells. In some people, however, these genes stop performing properly and begin growing and mutating abnormally. This increases the risk for breast cancer.

These abnormal gene mutations can be passed from generation to generation. If you’ve had a mother, grandmother, sister, or aunt with breast cancer or ovarian cancer, you’re more likely to have the mutated gene.

In fact, during their lifetime, women with a mutation in the BRCA1 or BRCA2 genes can have up to an 80 percent risk of being diagnosed with breast cancer. However, having the mutated gene doesn’t mean you’ll develop breast cancer.

A genetic test can tell you if you have mutated BRCA genes. It’s important to know that genetic testing is most helpful when you have a strong family history of either breast or ovarian cancer.

If you’d like to be tested, contact your doctor or your hospital’s education office. Ask for a recommendation for a genetic counselor. Make an appointment, and discuss the risks of having a BRCA genetic test.

Read more: A BRCA gene test saved my life, and my sister’s »

Your genes may affect your risk for breast cancer, but your lifestyle may have the greatest impact. Whether or not you have mutated genes, it’s important to lower your risk whenever you can.

These preventive measures may help you avoid a breast cancer diagnosis:

Maintain a healthy weight

Women who are overweight or obese may have a higher risk for developing breast cancer and other cancers related to mutated BRCA genes.

Eat well

A balanced diet can help you maintain a healthy weight, and it also provides your body with plenty of vitamins, minerals, and nutrients it needs to stay well.

Exercise regularly

Being physically active can help you achieve and maintain a healthy weight. Exercise also reduces your risk for certain diseases, including cancer, heart disease, and depression.

Stop smoking

People who smoke are more likely to develop breast cancer.

Reduce your alcohol consumption

Drinking alcohol, including wine, beer, and spirits, may increase your risk for breast cancer.

Learn more: Try this: 15 foods to help prevent breast cancer »