Metastatic Breast Cancer Treatment

Breast cancer becomes metastatic when cancer cells break away from the original tumor in the breast, travel through the bloodstream or lymphatic system and form new tumors in distant parts of the body, such as the bones, lungs, liver and brain. The metastasis process can occur months or even years after an initial breast cancer diagnosis. Though not considered curable in most cases, metastatic (stage 4) breast cancer is treatable. With ongoing therapy, many patients can live for years with advanced disease.

Symptoms of metastatic breast cancer can vary depending on the organs and tissues affected. Possible signs include persistent bone pain, fractures, shortness of breath, chronic cough, abdominal swelling, jaundice, headaches, neurological changes, unexplained weight loss and fatigue.

According to the American Cancer Society, breast cancer is the most frequently diagnosed cancer among women in the United States (aside from skin cancer). Though less common, it also affects men. While the majority of cases are detected at an early stage, approximately 6% of patients are diagnosed with metastatic disease at the outset, and a portion of those initially treated for early-stage breast cancer will later experience recurrence with distant spread.

Systemic therapy is the foundation of treatment for metastatic breast cancer. Unlike localized treatments that target a specific tumor site, systemic medications can travel through the bloodstream to reach widespread cancer cells. Treatment is individualized based on the biology of the tumor, including its hormone receptor (HR) and human epidermal growth factor receptor 2 (HER2) status, as well as the patient’s overall health and prior treatment history.

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Treatment options for metastatic breast cancer may include:

Hormone (endocrine) therapy for metastatic breast cancer

Approximately 65 to 75% of metastatic breast tumors are hormone-receptor positive (HR+), which means the cancer cells have receptors for estrogen or progesterone, making them sensitive to endocrine therapy. Therefore, hormone therapy—often combined with a targeted CDK4/6 inhibitor—is typically a first-line treatment unless there is a life-threatening condition, such as severe organ dysfunction (visceral crisis). The goal is to block or lower the levels of estrogen and progesterone, which can help prevent these hormones from fueling cancer growth.

Hormone therapy options for HR-positive metastatic breast cancer may include:

• Aromatase inhibitors, such as anastrozole, letrozole and exemestane
• Fulvestrant
• Ovarian suppression medications
• Tamoxifen

Though generally well tolerated, hormone therapy may cause side effects, such as hot flashes, joint pain, bone thinning and mood changes.

Targeted therapy for metastatic breast cancer

Targeted therapy focuses on specific molecular features of cancer cells, aiming to interfere with the pathways that promote tumor growth and survival. Targeted agents are frequently embedded into first- and second-line treatment regimens for HER2-positive and HR-positive disease, often given alongside endocrine therapy or chemotherapy.

Examples of targeted therapies for metastatic breast cancer include:

• CDK4/6 inhibitors, such as palbociclib, ribociclib and abemaciclib
• HER2-targeted drugs, such as trastuzumab, pertuzumab and trastuzumab deruxtecan
• PARP inhibitors, such as olaparib and talazoparib
• PI3K inhibitors, such as alpelisib

The specific drugs will be selected based on genetic testing and tumor profiling. Side effects of targeted therapy can vary by medication but may include diarrhea, fatigue, liver enzyme abnormalities, low blood cell counts and heart-related effects in some HER2-directed treatments.

Chemotherapy for metastatic breast cancer

Chemotherapy uses powerful medications to destroy rapidly dividing cells throughout the body, which can slow cancer spread and shrink tumors. Typically given in cycles, the drugs may be given intravenously or orally, either as a single agent or in a combined regimen.

Chemotherapy may be recommended for metastatic breast cancer that is hormone receptor-negative, HER2-negative or progressing despite other treatments. It may also be considered if the cancer is causing significant symptoms or affecting vital organs.

Chemotherapy drugs and drug combinations commonly used to treat metastatic breast cancer include:

• Capecitabine
• Carboplatin
• Docetaxel
• Doxorubicin
• Eribulin
• Gemcitabine
• Paclitaxel
• Vinorelbine

The specific chemotherapy plan will be determined based on the cellular makeup of the tumor, the location of the metastasis sites and the patient’s age, health and treatment history. Potential side effects include anemia, fatigue, hair loss, nausea, vomiting and increased risk of infection. Any discomfort can typically be managed with supportive medications and careful monitoring.

Immunotherapy for metastatic breast cancer

Immunotherapy aims to harness the power of the body’s own immune system to identify and destroy cancer cells. This innovative treatment approach may be considered for certain types of metastatic breast cancer, such as triple-negative breast cancer that expresses PD-L1, a protein that normally serves as a “brake” to prevent the immune system from attacking healthy tissues.

Immunotherapy drugs that may be used to treat metastatic breast cancer include:

• Atezolizumab
• Pembrolizumab

These medications are often combined with chemotherapy for enhanced treatment effectiveness.

Possible side effects of immunotherapy include fatigue, skin reactions, diarrhea and inflammation in organs such as the lungs, liver or thyroid. Because immunotherapy stimulates the immune system, it can sometimes cause the body to attack healthy tissues. For this reason, the patient will be closely monitored throughout treatment.

Radiation therapy for metastatic breast cancer

Radiation therapy uses high-energy beams to precisely target and destroy cancer cells. For metastatic breast cancer, radiation treatment is most often used to relieve symptoms and control tumor growth in a specific area of the body, such as the brain or a bone. For example, it may be administered to relieve bone pain, prevent fractures in a weakened bone or reduce the size of a tumor that is causing nerve compression or blocking a nearby organ.

Radiation delivery techniques for metastatic breast cancer may include:

• External beam radiation therapy (EBRT)
• Stereotactic body radiation therapy (SBRT)
• Stereotactic radiosurgery (SRS)
• Whole-brain radiation therapy (WBRT)

Side effects of radiation therapy can vary depending on the area of the body treated, but may include skin irritation, fatigue, localized hair loss and temporary worsening of symptoms due to inflammation.

Surgery for metastatic breast cancer

Surgery is not typically the primary treatment for metastatic breast cancer, a widespread disease that has spread from the breast to other parts of the body. However, it may be considered in certain situations to improve symptoms, stabilize a bone weakened by metastasis, relieve spinal cord compression or remove the primary breast tumor or an isolated metastatic tumor.

Surgical options for treating metastatic breast cancer may include:

• Lumpectomy
• Mastectomy
• Lymph node dissection
• Orthopedic stabilization surgery
• Metastasectomy (surgical removal of one or more metastases)

The risks and side effects of surgery can vary depending on the procedure performed, but may include pain, infection, bleeding, delayed wound healing and lymphedema. When planning the procedure, the surgical team will explain what the patient can reasonably expect in terms of recovery time and potential complications.

Clinical trials for metastatic breast cancer

Clinical trials allow scientists and clinicians to evaluate the effectiveness of novel treatments and new combinations of existing therapies compared to the current standard of care. These important research studies allow patient participants to benefit from innovative treatment options that are not yet widely available, while at the same time contributing to scientific progress and the advancement of cancer care.

Benefit from world-class care at Moffitt Cancer Center

If you would like to learn more about metastatic breast cancer treatment, you can request an appointment with a specialist in the Don & Erika Wallace Comprehensive Breast Program at Moffitt by calling 1-888-663-3488 or submitting a new patient registration form online. We do not require referrals.