Breast cancer occurs when cells in the breast change and start to grow out of control, according to the National Library of Medicine MedlinePlus resource. Cancer cells can metastasize—break away from their original location in the body and move through the blood or lymph nodes (structures in the body’s immune system) to other body parts to form new tumors, according to the NCI.
This leads to the most severe and incurable form of the disease, metastatic breast cancer, also called stage 4. Metastatic breast cancer most commonly occurs in your bones, liver, brain, and lungs, per the ACS.
Most cases of breast cancer are diagnosed in stages 1–3. Only about 6% are metastatic at diagnosis, according to NCI data from 2012-2018. From earlier stages, the disease can still metastasize, and does so in about 20–30% of cases, according to a November 2019 paper published in the journal BMC Cancer. Early diagnosis is crucial.
The number of cisgender women living with metastatic breast cancer in the US grew to more than 150,000 cases by the start of 2017, according to a May 2017 study published in the journal Cancer Epidemiology, Biomarkers & Prevention. Although the number of cases had increased, the survival rate doubled between 1992–1994 and 2005–2012—thanks to better screening and incredible advancements in treatment over the decades.
In general, changes in your DNA (genetic material) cause breast cancer, per MedlinePlus. These can be inherited or acquired through lifestyle and environmental factors.
Breast cancer spreads in multiple steps. Most cancer cells are eliminated as they travel through the body—only about 0.02–0.1% of tumor cells escape the body’s defense systems, per an August 2019 paper published in the journal Seminars in Cancer Biology. But if conditions are “favorable” throughout, these cells can form new tumors, per the NCI.
Metastasis can happen even if you got diagnosed or started treatment early. It's unclear why breast cancer spreads in certain people, according to the August 2019 paper.
There are several risk factors for breast cancer at any stage. These include, per MedlinePlus:
- Being assigned female at birth
- Older age
- Radiation or hormone therapy
- Obesity after menopause: Menopause is the cessation of one’s period for a year, without an underlying medical condition, per MedlinePlus.
- Alcohol consumption: Drinking the amount of alcohol equal to 3–6 glasses of wine per week was associated with a higher risk, per an October 2017 paper published in the journal Progress in Molecular Biology and Translational Science.
- Dense breast tissue: This can also make diagnosing breast cancer harder with a standard screening tool such as a mammogram, per the October 2017 paper.
- High exposure to estrogen (a hormone for female sex characteristics, per the NCI) through reproductive history features such as getting your period at an earlier age (before age 11) or starting menopause at an older age (55 or older), per the October 2017 paper.
- Having an inactive lifestyle
Metastatic breast cancer symptoms may vary depending on where your cancer has spread. These symptoms can also be caused by less serious conditions—such as mastitis, a common infection in people who are breastfeeding—or certain medications, per the NCI. But make sure to check in with your healthcare provider if you feel something is off.
The most common signs of metastatic breast cancer, regardless of where it has spread, per the ACS, are:
- Fatigue or feeling weak
- Unexplained weight loss
- Poor appetite
The most common symptoms that depend on where your cancer has spread are:
- Bone: New, unexplained pain in bones and joints (commonly seen in the hip or lower back), swelling, and bone fractures or breakages that appear to occur easier
- Liver: Certain digestive symptoms such as abdominal pain, vomiting, or nausea; jaundice (a yellowing of the skin); itchy skin; and a rash
- Lungs: Shortness of breath and cough, and chest pain
- Brain: Headaches that persist and get progressively worse, dizziness, speech or vision problems, vomiting or nausea, seizures, behavioral changes, and memory issues
Diagnostic methods may vary depending on where the healthcare provider thinks your cancer may have spread. Tests also differ depending on whether you have a history of breast cancer. Below are the common types of tests used to diagnose metastatic breast cancer.
- Imaging tests: These can include MRI, CT, X-ray or ultrasound, or PET scans. The imaging test your provider chooses depends on your cancer’s potential location.
- Blood tests: These can show tumor proteins (also called tumor markers or biomarkers) in the blood, though the biomarkers aren’t always due to cancer, per the American Society of Clinical Oncology (ASCO).
- Biopsies: During this procedure, a specialist removes and examines your cells or tissues from suspected areas, per the NCI.
In most cases, a diagnosis begins when you have a history of breast cancer and report a new, unusual symptom to your provider. This prompts tests and imaging. If you have previously had breast cancer and have worsening leg or knee pain, for example, your healthcare provider might order an X-ray and bone scan to check for cancer lesions in those areas. Not every person who has breast cancer and worsening pain in another area has developed metastatic breast cancer.
An earlier-stage breast cancer diagnosis may look different, so if you don’t have a history of breast cancer and then experience symptoms, your healthcare provider may choose to start with other tools, as well as breast-specific biopsies and blood tests. The provider would then conduct tests to determine the stage. Initial tests can include, per MedlinePlus:
- Physical exam: A clinical breast exam can check for unusual lumps or other signs in the breasts and armpits.
- Medical history: You can inherit the risk of breast cancer.
- Breast-specific imaging tests: These include a mammogram, ultrasound, or MRI. Regular mammograms are essential for women who are more than 45 years old (or more than 30 years old if your provider determines you’re at high risk) regardless of symptoms, per the ACS.
No cure for metastatic breast cancer exists, but an increasing number of treatment options may prolong or improve your quality of life. The treatments for metastatic breast cancer are the same types as those used to treat earlier stages of breast cancer, per the NCI.
Metastatic breast cancer treatment depends on its subtype and whether you are premenopausal or postmenopausal.
You may also be able to join clinical trials for new treatment methods and medications. And you can receive multiple types of treatment at the same time.
Some examples of treatments include, per the NCI:
- Hormone therapy: Hormones can cause certain types of cancer to grow, so this therapy involves removing or blocking these hormones.
- Chemotherapy: This treatment uses drugs to stop the growth of cancer cells. You may receive chemotherapy by mouth or through the vein. The medication can then affect cancer cells throughout the body, either killing them or stopping them from dividing.
- Radiation therapy: Providers use x-rays or other types of radiation to kill or prevent the growth of cancer cells.
- Targeted therapy: This treatment attacks specific cancer cells so it is less harmful to normal cells than chemotherapy or radiation therapy.
- Surgery: Cancer can be removed from specific organs, sometimes followed by radiation therapy.
- Chemotherapy and immunotherapy: This combines chemotherapy with a treatment that uses your immune system to fight cancer.
You may also receive palliative care—special treatment or medical care for symptoms and discomfort of a serious illness such as cancer, per the National Institute on Aging. Palliative care providers help you manage side effects from cancer treatment or other cancer-related issues.
You can help reduce your risk of breast cancer through lifestyle changes, though there is no sure way to prevent the disease. Here are some things you can do to reduce your risk of breast cancer, per MedlinePlus:
- Maintain a healthy weight as you transition through menopause, per the October 2017 paper
- Reduce alcohol use
- Limit your exposure to estrogen
If you have a high genetic risk of breast cancer you may also speak with your healthcare provider about taking specific medications or getting a mastectomy—surgery to remove part or all of the breast.
Regular screenings such as mammograms and the right treatment at an earlier stage of breast cancer can help prevent the spread, but nothing can guarantee cancer doesn’t metastasize. If you experience any signs of breast cancer, or if you have a history of breast cancer and notice new symptoms, reach out to a healthcare provider right away.