Metastatic breast cancer (MBC), also known as Stage IV breast cancer, is the most advanced form of breast cancer. It occurs when cancer cells from the breast spread to other parts of the body, such as the bones, liver, lungs, or brain. Despite being the least understood and most underrepresented stage in public discourse, MBC affects hundreds of thousands of people globally and remains a leading cause of cancer-related deaths among women. 

What is Metastatic Breast Cancer?

Metastatic breast cancer occurs when breast cancer cells break away from the original tumor and spread through the bloodstream or lymphatic system to distant organs. While breast cancer is often treatable in its early stages, once it has metastasized, it becomes chronic and requires ongoing treatment to manage symptoms and progression.

People with MBC are never “cured” of their cancer, though they may live for many years with the disease. The focus of treatment shifts from eradication to controlling the spread and improving quality of life. Though incurable, metastatic breast cancer can be managed as a chronic illness with treatment plans designed to extend survival and minimize symptoms.

The process of metastasis involves several stages:

1. Local Invasion: Cancer cells spread from the original tumor site to nearby tissue.
2. Intravasation: Cancer cells enter the bloodstream or lymphatic system.
3. Survival in Circulation: Cancer cells travel through the body via blood or lymphatic fluid.
4. Extravasation: Cancer cells exit the bloodstream or lymphatic system and invade a new organ.
5. Colonization: Cancer cells begin to grow in the new location, forming secondary tumors.

While breast cancer can metastasize to any part of the body, the most common sites are the bones, lungs, liver, and brain. Bone metastasis is the most frequent and can cause significant pain, fractures, and mobility issues.

Metastatic breast cancer can develop from any type of breast cancer, but certain factors increase the likelihood of metastasis. These include:

1. Type of Breast Cancer: Aggressive forms, such as Triple Negative Breast Cancer (TNBC) or HER2-positive breast cancer, have a higher risk of metastasis.
2. Late-Stage Diagnosis: Patients diagnosed at later stages (Stage II or III) are more likely to experience metastasis.
3. Recurrence: Some people with early-stage breast cancer may experience a recurrence that metastasizes. Even those who have been cancer-free for years may later develop metastatic disease.
4. Age and Race: While breast cancer is most common in older women, younger women, especially African American and Latina women, have a higher risk of developing aggressive and metastatic forms of the disease. Black women in particular are more likely to be diagnosed with metastatic breast cancer and face a higher mortality rate.

Symptoms of MBC vary depending on where the cancer has spread:

• Bone Metastasis: Persistent pain in the bones, fractures, and decreased mobility.
• Liver Metastasis: Jaundice (yellowing of the skin and eyes), abdominal swelling, and fatigue.
• Lung Metastasis: Shortness of breath, persistent cough, and chest pain.
• Brain Metastasis: Headaches, vision changes, seizures, and difficulty with balance or speech.

These symptoms often mimic other common health issues, making it essential for patients to maintain regular communication with their healthcare providers to monitor for changes in their health.

When breast cancer spreads, it is still considered breast cancer, even if it is found in other parts of the body. For example, if breast cancer cells spread to the liver, it is not liver cancer but metastatic breast cancer to the liver.

Diagnosis of MBC involves imaging tests such as CT scans, PET scans, MRIs, or bone scans, along with biopsies of the metastatic sites to confirm that the cancer originated in the breast.

The treatment of metastatic breast cancer is complex and varies based on factors like the location of the metastases, the biology of the cancer, and the patient’s overall health. Treatment is usually aimed at managing symptoms and slowing the progression of the disease. Common treatments include:

1. Hormonal Therapy: For hormone receptor-positive (HR+) cancers, hormonal therapies like tamoxifen or aromatase inhibitors can help slow tumor growth by blocking estrogen or lowering estrogen levels in the body.

2. Targeted Therapy: Drugs like trastuzumab (Herceptin) target specific proteins (like HER2) found in some breast cancers, helping to slow their growth. Other targeted therapies, such as CDK4/6 inhibitors (palbociclib), work by interfering with the cancer cells’ ability to divide.

3. Chemotherapy: Chemotherapy may be used when other treatments are no longer effective or when the cancer is aggressive. It works by killing rapidly dividing cancer cells but can also cause significant side effects.

4. Immunotherapy: For patients with TNBC, immunotherapy has emerged as a promising treatment option, helping the body’s immune system to better recognize and attack cancer cells.

5. Radiation Therapy: Radiation may be used to relieve pain or symptoms caused by metastasis to the bones or brain.

6. Clinical Trials: For many patients, participating in clinical trials offers access to cutting-edge treatments that are not yet widely available. Research into new drugs and combinations of therapies is ongoing.

According to the American Cancer Society, approximately 30% of women diagnosed with early-stage breast cancer will develop metastatic disease. The 5-year relative survival rate for metastatic breast cancer is about 29%, though it varies significantly depending on the location of metastases and the patient’s overall health.

However, these statistics do not tell the full story. Many people with MBC live for years with the disease, and treatment advancements continue to improve survival rates and quality of life. Newer therapies, such as targeted treatments and immunotherapy, have contributed to better outcomes for patients with certain types of metastatic breast cancer.

Despite advancements in breast cancer research, metastatic breast cancer remains underfunded, receiving only a fraction of the total breast cancer research budget. This disparity is critical because curing breast cancer hinges on understanding and effectively treating metastasis. Advocates call for increased funding for MBC-specific research to develop better treatments, prolong life, and ultimately find a cure.

Living with MBC requires physical, emotional, and financial support. Many people with MBC face the challenge of managing ongoing treatments, dealing with the unpredictability of the disease, and coping with the emotional toll of a terminal diagnosis.

Supportive care services, including palliative care, can help manage symptoms and improve quality of life. Additionally, organizations like METAvivor and Living Beyond Breast Cancer provide resources for patients, caregivers, and families, advocating for increased awareness, funding, and support.

Metastatic breast cancer affects tens of thousands of people worldwide, many of whom live with the disease for years. While progress has been made in treatment and research, there is still much work to be done to improve outcomes for those with MBC. As the breast cancer community continues to advocate for awareness, funding, and new therapies, it is crucial to remember that metastatic breast cancer is not the end of the fight, but a different battle requiring ongoing care, attention, and support.

By sharing the stories of those living with MBC and pushing for more research and awareness, we can help bring hope and better outcomes to patients and their families.