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Understanding MBC > What Is MBC?

What is MBC?

Breast cancer starts when cells in the breast do not work the way they should and grow out of control. When this happens, the cells can build up to form a malignant (cancerous) tumor.1,2 Metastatic breast cancer (MBC) happens when those cells spread to other parts of the body.3 Common parts of the body where the cancer may spread include the bones, brain, lungs, and liver.4 MBC is sometimes called advanced or stage 4 cancer.3,4 Although MBC has spread to another part of the body, it's still breast cancer and treated as breast cancer.3 About 30% of women diagnosed with early stage breast cancer will develop metastatic disease.4 And although it is rare, male breast cancer represents approximately 1% of all breast cancers worldwide.15

Symptoms of MBC

The symptoms of metastatic breast cancer depend on where the cancer has spread to and how large it is. If the cancer has spread, it can cause symptoms in specific areas.5 For instance, bone metastases can cause bone pain, although bone pain may also be a drug side effect.5,6 Cancer that has spread to the lungs can cause shortness of breath.5 These are some of the signs that breast cancer has spread5:

  • Pain in the back, neck, bones, or joints
  • Broken bones
  • Swelling
  • Headaches
  • Seizures
  • Dizziness
  • Confusion
  • Changes to vision, such as double vision, or vision loss

Talk to your doctor if you have any of these symptoms. Good communication can help you and your doctor figure out what may be causing any symptoms.

Stages of breast cancer

Learning about the different stages of breast cancer may help you feel more prepared as you continue to communicate with your doctor and manage your symptoms.

Breast cancer is considered recurrent when the original cancer has come back after treatment. It can come back months or years after it has been treated. Once it has spread to another part of your body, it is known as recurrent metastatic breast cancer.4,7

When your first diagnosis is metastatic breast cancer, it means that the cancer has already spread to another part of your body before it was found in your breast.4 Your doctor may call this de novo metastatic breast cancer. De novo means from the beginning. In the US, about 6% to 10% of women have metastatic breast cancer when they are first diagnosed.8

When doctors diagnose breast cancer, they give it a stage from 0 to 4. The stage is based on the size of the tumor and whether it has spread to the lymph nodes or other parts of the body. The higher the stage, the more likely that9:

  • The tumor is larger
  • The cancer has spread to other parts of the body or to the lymph nodes (small bean-shaped glands that are a part of the immune system and found throughout the body)9,10

You may also hear the terms advanced, metastatic, recurrent, or progression. Here is a breakdown of what those terms can mean.

If you hear… It may mean that the cancer…
  • Is stage 3 or stage 4
  • Has started in the breast but has spread to nearby tissues or lymph nodes or another part of the body
  • Can be considered metastatic (in certain instances)
  • Is stage 4
  • Has started in the breast but has spread to another part of the body
  • Can be described as advanced
  • Was treated
  • Came back in the same place as the original cancer (local recurrence) or spread to other areas of your body (distant recurrence); can happen months or years after treatment12
  • Can be called metastatic


  • Is continuing to grow or spread

While metastatic breast cancer might not completely go away, there are a wide variety of treatment options. Treatment might control the cancer, sometimes for many years. If a treatment is no longer working, there is usually something else to try.4 A person might have active cancer at times or have cancer that is in remission at other times.4,13,14 Many different treatments—alone, in combination, or in a sequence—are often used to slow the progression of the disease.4

Course of breast cancer

Several things affect the course (prognosis) of breast cancer, such as the stage of breast cancer and how fast it is growing.15 If the breast cancer is advanced, the treatment options and goals are different than if it were in an early stage.3

Treatment for metastatic breast cancer focuses on slowing the growth or spread of cancer. It can help reduce the symptoms that get in the way of your daily routine, so you are able to do the things you enjoy. Treatment can also prolong your life.14

Biomarker testing may help your healthcare team determine the appropriate treatment plan for your type of cancer.15

Types of MBC

There are different subtypes of metastatic breast cancer.16

Laboratory tests can help your doctor find out what subtype you have. Knowing your breast cancer subtype can help determine your treatment.16

Hormone receptor-positive

Breast cancers that express hormone receptors are called “hormone receptor-positive” (HR+). Hormone receptors are proteins found in and on cells.16

There are two kinds of hormone receptors: estrogen receptors (ER) and/or progesterone receptors (PR).16

  • Breast cancers that have estrogen receptors are called “ER-positive” (ER+)
  • Breast cancers that have progesterone receptors are called “PR-positive” (PR+)

If the cancer does not have ER (ER-) or PR (PR-), it is called “hormone receptor-negative.”16


  • HER2 (human epidermal growth factor receptor-2) is a gene that helps control how cells grow and divide. The HER2 gene makes HER2 proteins17
  • Breast cancer cells that have many copies of the HER2 gene or high levels of HER2 protein are called “HER2- positive” (HER2+). HER2-positive breast cancers grow more quickly.16 They can also be either hormone receptor-positive or hormone receptor-negative
  • Cancers with no or low levels of the HER2 protein and/or few copies of the HER2 gene are called “HER2- negative” (HER2-)16


Breast cancer that does not express ER, PR, and HER2 (ER-, PR-, HER2-) is called “triple-negative.” This type of breast cancer seems to be more common among younger women. Triple-negative breast cancer may grow more quickly.16

About 30% of women diagnosed with early-stage breast cancer will develop metastatic disease.18


  1. American Cancer Society. Caregiver resource guide. org/cancer-control/en/booklets-flyers/american-cancer-society-caregiver-resource-guide.pdf. Accessed November 4, 2019.
  2. National Cancer Institute. Malignant. NCI Dictionary of Cancer Terms. Accessed November 2, 2019.
  3. American Cancer Society. Understanding advanced cancer, metastatic cancer, and bone metastasis. Accessed November 15, 2019.
  4. Metastatic breast cancer. Accessed November 7, 2019.
  5. American Society of Clinical Oncology. Breast cancer - metastatic: symptoms and signs. Accessed December 1, 2019.
  6. Bone Pain. Managing Side Effects Accessed November 29, 2019.
  7. Recurrent breast cancer. Accessed November 7, 2019.
  8. Metastatic Breast Cancer Network. Incidence and incidence rates. incidence-rates/. Accessed September 5, 2019.
  9. American Joint Committee on Cancer. What is cancer staging?, November 29, 2019.
  10. National Cancer Institute. Lymph node. NCI Dictionary of Cancer Terms. Accessed November 29, 2019.
  11. Cancer Research UK. About advanced cancer. cancer/breast-cancer/stages-types-grades/advanced/about. Accessed December 5, 2019.
  12. Mayo Clinic. Recurrent breast cancer. conditions/recurrent-breast-cancer/symptoms-causes/syc-20377135?p=1. Accessed November 29, 2019.
  13. National Cancer Institute. Remission. NCI Dictionary of Cancer Terms. terms/search?contains=false&q=remission. Accessed September 5, 2019.
  14. National Cancer Institute. Breast cancer treatment (PDQ®)–health professional version. Accessed December 2, 2016.
  15. Gucalp A, Traina TA, Eisner JR, et al. Male breast cancer: a disease distinct from female breast cancer. Breast Cancer Res Treat. 2019;173(1):37-48.
  16. National Cancer Institute. Breast cancer treatment (PDQ®)–patient version. Accessed June 26, 2019.
  17. American Society of Clinical Oncology. Breast cancer - metastatic: introduction. Accessed July 13, 2018.
  18. HER2 status. Symptoms & Diagnosis. Accessed June 18, 2019.
  19. Metastatic breast cancer. Symptoms & Diagnosis. Accessed July 13, 2018.
  20. National Cancer Institute Dictionary of Cancer Terms. Accessed January 29, 2021.