As a cell grows and divides, it makes copies of its DNA. Sometimes the DNA in the new cell is different from the original cell. This is called a mutation.
You can be born with a genetic, or hereditary, mutation that you inherit from your mother or father. If one of them was born with one in one of their genes, there's a 50-50 chance they'll pass it on to you. That’s because they could pass on either their healthy gene or the altered one.
Studies suggest that about 5% to 10% of all breast cancer diagnoses are due to this type of change. The most common hereditary ones are BRCA1 and BRCA2.
An acquired mutation happens after birth. The cell can make a mistake as it copies its DNA when it divides. Things in the environment like radiation or chemicals can also cause a change.
When a cell builds up too many harmful genetic changes and these damaged cells survive, it can start to grow and divide faster than it should. This is how cancer starts.
Genetic Mutations and Breast Cancer
Your doctor will test your tumor to see if its cells have changes in a gene called HER2. These changes cause the gene to make too much of the HER2 protein. When cells have too much of this protein, the tumor is HER2-positive. If they don’t, it’s HER2-negative.
About 10% to 20% of breast cancer patients have a tumor that tests HER2-positive. These tumors often spread faster than HER2-negative ones and are more likely to come back after treatment. If your cancer is this type, your doctor can treat it with drugs that target and block the HER2 proteins. These targeted therapies can be very effective.
The most common hereditary mutations found in people with breast cancer are in the BRCA1 and BRCA2 (BReast CAncer 1 and 2) genes.
These genes help cells fix mistakes that can happen each time they grow and divide. If you have a BRCA1 or BRCA2 mutation, that gene doesn’t fix these errors well.
Because BRCA stands for breast cancer, it’s easy to think BRCA mutations only increase breast cancer risk. But the mutations are found in every cell in your body. BRCA mutations also increase the risk for pancreatic cancer, ovarian cancer, prostate cancer, and melanoma (a dangerous type of skin cancer).
The most common breast cancer gene after BRCA1 and BRCA2 is one called PALB2. It works with the BRCA2 gene to repair DNA errors that can happen during cell division. (PALB2 is short for “partner and localizer of BRCA2.”) An abnormal PALB2 gene makes it 5 to 9 times more likely that you’ll get breast cancer.
Tumor Testing in Advanced Breast Cancer
If your breast cancer comes back after treatment or spreads, your doctor will want to have your tumor’s HER2 status tested again. That’s because as cancers grow, they can change from HER2-positive to HER2-negative or HER2-negative to HER2-positive. If yours changes its HER2 status, you may have new treatment options.
Your doctor may also want to do other tests on your tumor.
If you have a family history of this disease, your doctor may suggest you get genetic testing. This can tell you if you were born with a genetic change that raises the chances that you’ll get cancer. If you have a hereditary mutation, it doesn’t mean you will get cancer. But you will want to learn more about ways to lessen your risk.