
Metastatic breast cancer, also called MBC, is cancer that began in the breast, but has spread to another part of the body and formed other malignant growths. The most common areas for breast cancer to spread to are the lungs, liver, bones, and brain. Many people who are diagnosed with MBC have been treated for non-metastatic breast cancer in the past. But many others are diagnosed with MBC without a previous diagnosis of breast cancer.
If you or a loved one has recently been diagnosed with MBC, you are likely wondering what happens next. The following is an overview of the steps to take when working with the healthcare providers (HCPs) who diagnose and treat MBC.
Follow up with diagnostic tests
The initial diagnosis of MBC is typically followed by a number of additional tests that may include biopsies of the primary and secondary tumors, blood work, and imaging tests such as MRIs, PET scans, X-rays, and others.
While testing will vary from person to person, the diagnostic tests should answer these questions:
- What areas has the cancer spread to?
- What is the size of the tumors?
- What is the grade of the cancer cells? (Grading determines how much the cancer cells have mutated, which is often an indicator of how malignant the tumors are and how quickly the cancer will spread).
- How aggressively is the cancer growing and spreading?
- What effect are hormones (estrogen/progesterone) and growth factors (human epidermal growth factor receptors, or HER2) having on tumor growth?
The aim of diagnostic tests is to give you, your loved one, and your HCPs a clear and detailed look at the cancer, which will help determine the best course for treatment. Because each case of MBC is somewhat unique, treatment for MBC is individualized.
Get copies of the test results
You will want to get copies of the test results, pathology reports, and other documents regarding the diagnosis, treatment, and medical history. These will make the process much easier if you or your loved one decide to see a different HCP in the future.
Get a second opinion
You may want to seek a second opinion for the diagnosis. A second opinion is when a patient sees a different HCP to be examined and evaluated. This is sometimes done because a person is unsatisfied with a treatment or the treatment recommended by their current HCP, but there are a variety of reasons to seek a second opinion when diagnosed with MBC:
- You may want to see a specialist who is experienced in treating similar cases of MBC.
- You may be looking for a new perspective on the diagnosis and the treatment possibilities.
- You may want to gain access to a clinical trial for a new type of treatment.
Since treatment for MBC will be an ongoing process, it is very important that you and your loved one work with HCPs whom you trust and who understand your needs.
Choose and start a treatment
Treatment options will depend on the type, location, medical history, and a number of other factors. Deciding on a treatment plan will be done under the guidance of HCPs. As mentioned above, treatment is tailored to meet a person's individual needs. While there is currently no cure for MBC, there are numerous treatment options available that work to halt the progress of cancer, minimize symptoms, improve quality of life, and prolong life. It’s estimated that there are more than 150,000 people in the United States living with MBC.
Sources: Merck Manual. Breast Cancer Overview. Ap... + 6
- Merck Manual. Breast Cancer Overview. April 2025.
- Breastcancer.org. Metastatic Breast Cancer. July 2, 2025.
- InformedHealth.org [Internet]. Cologne, Germany: Institute for Quality and Efficiency in Health Care (IQWiG); 2006-. Overview: Metastatic breast cancer. [Updated 2024 Jan 23].
- Metastatic Breast Cancer Network. For the Newly Diagnosed. Accessed May 27, 2026.
- Living Beyond Breast Cancer. Getting a Second Opinion. Accessed May 27, 2026.
- National Cancer Institute. Metastatic Breast Cancer Survival Rates. May 18, 2017.
- Gallicchio L, Devasia TP, et al. Estimation of the Number of Individuals Living With Metastatic Cancer in the United States. J Natl Cancer Inst. 2022 Nov 14;114(11):1476-1483.


