Metastatic breast cancer: When cancer spreads beyond the breast

By Nicole Brudos Ferrara

Breast cancer stages range from 0 to 4, with 0 indicating cancer that is noninvasive or contained within the milk ducts. "Metastatic breast cancer is what we define as stage 4 disease," says Lida Mina, M.D., a Mayo Clinic medical oncologist specializing in breast cancer. "It is breast cancer that has traveled outside the breast and the lymph nodes and attacked other distant organs."

Female breast cancers are diagnosed at stage 4 in less than 10% of cases, but up to 30% of people diagnosed with early stage breast cancer can progress to metastatic disease. Today, an estimated 168,000 people in the U.S. live with metastatic breast cancer.

While metastatic breast cancer is often incurable, Dr. Mina says researchers have advanced treatments for the disease, allowing people to live longer with a better quality of life. If you’ve been diagnosed with metastatic breast cancer, here’s what she wants you to know:

Genetic testing can help guide your treatment.

Your care team will assess your family history and environmental exposures to determine if you should undergo testing for a genetic predisposition to breast cancer, such as BRCA, or other hereditary mutations, says Dr. Mina.

Some treatments work better in patients with specific mutations in breast cancer genes, which can help guide your care. Genetic test results can also help you understand if you — and potentially your family members — are at increased risk of breast and other cancers.

Your care team will also test tissue from a biopsy of your cancer to determine your breast cancer type, which is based on:

• The part of the breast in which your cancer began (milk ducts, milk-producing lobules or connective tissues).
• How your cancer cells look under a microscope (their shape and their degree of difference from typical cells).
• Whether your cancer cells are fueled by hormones (estrogen and progesterone) or driven by other growth hormones, such as HER2 protein.

Your tissue will be used to sequence your cancer's DNA so your care team can study its biology and genetic makeup. "We take tissue from a biopsy or do a blood liquid biopsy, and we do full next-generation sequencing testing to try to find targets we can tailor treatment to," says Dr. Mina.

Understanding your breast cancer type can help healthcare professionals develop a tailored treatment plan for your cancer. Treatment for metastatic breast cancer often involves drugs called systemic therapies, including chemotherapy, hormone therapy, targeted-drug therapy and immunotherapy.

Your care team should include breast cancer experts from various medical disciplines.

Seek care at a comprehensive cancer center that can offer a team of experts to guide your treatment, says Dr. Mina. "For metastatic breast cancer treatment, I think the biggest strength is to have experts from multiple disciplines on the care team. For example, if a patient's cancer has metastasized to bone, it is important to involve radiation, orthopedics, palliative care and integrative medicine to offer the patient a comprehensive approach."

Dr. Mina also emphasizes the importance of having a pain expert on the care team. "Pain should always be controlled. There is no reason for patients to suffer. Patients should be vocal about their pain."

To ensure you’re maintaining the highest possible quality of life, Dr. Mina recommends asking your care team these questions about their proposed treatments: Will this treatment negatively affect my quality of life? If a treatment has challenging side effects, will it provide more good days in the long run? If not, is it worth it? "With metastatic breast cancer, it’s always about balancing the risks and the benefits," she says.

Clinical trials may offer promising new treatments.

Clinical trials designed to test new drugs may offer new options for people with metastatic breast cancer. "A clinical trial is an amazing opportunity. But there are also risks because we don’t know if a patient’s cancer will respond to the treatment being tested," says Dr. Mina. "Many patients with breast cancer participate in clinical trials because they know that even if it doesn’t benefit them, it will help advance the science and help other patients in the future. They are truly selfless."

Dr. Mina and other researchers are investigating drugs that target breast cancer cells’ resistance to treatment. "Metastatic breast cancer is still not curable because the cancer cells adapt and develop resistance. So, many clinical trials for metastatic breast cancer are studying ways to bypass that resistance." For example, if a cancer is estrogen receptor-positive, its cells have receptors that allow them to use the hormone estrogen to grow. Dr. Mina says researchers are investigating the pathways of estrogen receptor resistance to find drugs that can target those pathways and overcome that resistance.

Another promising treatment for metastatic breast cancer is chimeric antigen receptor-T cell therapy (CAR-T cell therapy), a form of immunotherapy in which a person’s T cells — white blood cells involved in the immune system response — are genetically modified to produce chimeric antigen receptors (CARs). These CAR-T cells are infused into the patient's bloodstream to target and kill cancer cells.

Dr. Mina is working with fellow researchers to launch a clinical trial investigating CAR-T cell therapy for metastatic breast cancer. A CAR-T cell therapy trial for people with triple-negative breast cancer — tumors that are estrogen-receptor negative, progesterone-receptor negative and hormone-receptor negative — is already underway at Mayo Clinic.

Dr. Mina wants people diagnosed with metastatic breast cancer to know that the disease can be treated. "We have come a long way. Many advances have made the disease treatable, even if it's not curable, providing better quality of life."

Learn more

Learn more about metastatic breast cancer and find a clinical trial at Mayo Clinic.

Join the Breast Cancer Support Group on Mayo Clinic Connect.

Also, read these articles:

• "Breast cancer types: What your type means"
• "HER2-positive breast cancer: What is it?"
• "Is a cancer clinical trial right for me?"
• "9 common questions about genetic testing for cancer"
• "Liquid biopsy can help guide cancer treatment"
• "Immune checkpoint inhibitors: Immunotherapy for people with triple-negative breast cancer"
• "4 things you can do to improve your quality of life after breast cancer"
• "The 4 types of systemic therapy for breast cancer"