Understanding Gene Mutations in Your Metastatic Breast Cancer Diagnosis Is Crucial to Your Treatment

"It's really important that patients ask their doctor about the opportunity for genetic testing of their tumor. Genetic mutations may be relevant to the first-line treatments they receive and treatments they receive when and if that first drug no longer works," Elizabeth Comen, MD, a breast medical oncologist at Memorial Sloan Kettering Cancer Center in New York, tells SurvivorNet.

The Genetics of a Breast Tumor

You were born with genes that you inherited from your parents. Tumors have their own set of genes. Some of the genes are the same as the genes of the person carrying the tumor. But, others are unique to the tumor and, more importantly, they may help the tumor grow.

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Targeted drugs, which are available for many different types of cancers, can shut down or greatly weaken certain genes that help tumors grow. Doctors need to know the genetic makeup of your breast tumor in order to know whether any of these medications would work for you.

Genes that Drive Cancer & Treatment Decisions

In HER2-positive breast cancer, the human epidermal growth factor receptor 2 (HER2) gene in the tumor produces higher than normal levels of a protein by the same name. Targeted drugs, including Herceptin (Trastuzumab) and several others, can block this gene and prevent the cancer from progressing.

Dr. Comen discusses treatment for HER2+ metastatic breast cancer.

About 30 to 40 percent of breast cancers have a mutation in a gene called PIK3CA that helps tumors grow. These mutations happen in hormone-receptor positive, HER2-negative breast cancers. Drugs that disable this gene in the tumor can halt the progress of the breast cancer. People whose breast cancer has the PIK3CA mutation take a drug that targets the gene in addition to hormone therapy that treats hormone-receptor positive cancers.

Related: FDA Approves Promising New Drug for PIK3CA+ Breast Cancer

People who have a BRCA1/2 mutations that's a mutation in your own DNA, not the tumor's benefit from drugs called PARP inhibitors. These medications make it difficult or impossible for cancer cells to repair themselves, which causes the cells to die.

Dr. Heather McArthur talks PARP inhibitors for metastatic breast cancer.

Clinical trials currently in progress are exploring numerous other gene mutations in breast tumors and medications that could disable those genes.

Advocate For Yourself

To make sure that you get any gene-targeted drugs that may help you, take the following actions:

• Ask if your doctors have already tested your tumor for genetic mutations.
• If your tumor hasn't yet had genetic testing, ask for testing at diagnosis and, if it happens, progression of metastatic breast cancer. There's a few good reasons for this. First, Comen says, “If you didn't have any mutations at diagnosis, new mutations may have evolved when the disease progresses," Comen says. Further, mutations could point to currently available drugs or could make you eligible for clinical trials testing new drugs or new uses for existing drugs.
• Ask if your doctor has considered you for any clinical trials at your health care facility or others.  If your tumor doesn't have any gene mutations suited for currently available mutations, you could have mutations appropriate for drugs in clinical trials.

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