When breast cancer spreads beyond the breast and nearby lymph nodes, it is referred to as metastatic breast cancer, also known as stage IV. When these cancer cells form new tumors in the bones, it’s called bone metastasis or bone mets. These bone tumors contain breast cancer cells, not primary bone cancer cells, so they are treated with breast cancer therapies. This spread happens when breast cancer cells detach from the original tumor and enter the bloodstream or lymphatic system, traveling to distant parts of the body. Bones are the most common site for breast cancer to metastasize.
Symptoms and Diagnosis of Bone Metastases
Bone pain is often the first symptom of breast cancer that has spread to the bones. This persistent ache may worsen with activity, often not subsiding with rest and disrupting sleep. Unexplained fractures can also occur, as bones become fragile and break from minor injuries or without trauma. If cancer spreads to the spine, it can compress the spinal cord, leading to back or neck pain, numbness or weakness in the legs, and issues with bladder or bowel control.
To diagnose bone metastases, healthcare providers use imaging tests. A bone scan involves injecting a radioactive substance into a vein, highlighting areas of increased bone activity. PET and CT scans offer detailed images to locate and assess metastatic lesions. X-rays and MRIs are also used; MRIs are effective for early detection and provide clear images of bone and soft tissues. A biopsy of the suspicious bone area may confirm breast cancer cells and analyze their characteristics.
How Breast Cancer Interacts with Bone Tissue
Bone tissue undergoes continuous remodeling, where old bone is broken down and new bone is formed to maintain strength. This involves two cell types: osteoclasts, which break down bone, and osteoblasts, which build new bone. In healthy bone, their activities are balanced for proper maintenance.
When breast cancer cells metastasize to bone, they disrupt this balance, leading to two primary types of bone lesions. Osteolytic lesions, most common with breast cancer, occur when cancer cells accelerate osteoclast activity, causing excessive bone breakdown without adequate new bone formation. This creates weak spots or holes, increasing pain and fracture risk. Conversely, osteoblastic lesions involve cancer cells stimulating osteoblasts to produce new bone. This new bone is disorganized and structurally weak, despite appearing denser on scans. Both lesion types compromise bone strength and can lead to complications.
Treatment Approaches for Bone Metastases
Treatment for breast cancer bone metastases combines therapies to control cancer, manage symptoms, and preserve bone health. A multidisciplinary team integrates these approaches.
Systemic Therapies
Systemic therapies are drugs that travel through the bloodstream to treat cancer cells throughout the body, including those in the bones. These treatments are foundational for managing metastatic breast cancer.
Hormonal therapy is used for hormone receptor-positive breast cancers, blocking hormones like estrogen and progesterone that fuel cancer growth. Chemotherapy uses powerful drugs to kill rapidly dividing cancer cells, shrinking tumors and alleviating symptoms. Targeted therapies focus on specific proteins or pathways within cancer cells that promote growth or spread, such as those in HER2-positive breast cancer. Immunotherapy leverages the body’s own immune system to recognize and destroy cancer cells.
Bone-Modifying Agents
Bone-modifying agents (BMAs) are a significant treatment component, designed to protect and strengthen bones affected by cancer. Bisphosphonates (e.g., zoledronic acid, pamidronate) inhibit osteoclast activity, slowing bone breakdown. Denosumab (Xgeva), another BMA, targets RANKL, a protein promoting osteoclast formation, effectively reducing bone destruction. These agents reduce bone pain, lower fracture risk, and manage high blood calcium levels (hypercalcemia) from bone breakdown. Patients beginning BMA treatment undergo a dental evaluation due to a rare but serious side effect: osteonecrosis of the jaw.
Local Therapies
Local therapies target specific bone areas to alleviate symptoms and prevent complications. Radiation therapy delivers targeted radiation to bone lesions, effectively relieving pain, often within days to weeks. Radiation also strengthens osteolytic lesions by promoting recalcification, reducing fracture risk in the treated area. Surgery may stabilize a bone at risk of fracture or repair a broken one.
Managing Complications and Maintaining Quality of Life
Living with bone metastases requires proactive management of potential complications to maintain quality of life. This involves a coordinated approach with various specialists.
Pain Management
Managing bone pain extends beyond systemic cancer treatments and bone-modifying agents. Pain medications include non-opioids (e.g., paracetamol, anti-inflammatory drugs), progressing to stronger opioid-based medications if needed. Nerve pain can be addressed with specific medications (e.g., certain antidepressants, anti-seizure drugs, or localized lidocaine patches). Palliative care specialists can also provide comprehensive pain management strategies and supportive care.
Fracture Prevention and Care
Preventing fractures is a primary focus, as weakened bones are susceptible to breaks. Orthopedic surgeons stabilize bones at high risk of fracture or those already fractured. This may involve surgical procedures to insert metal rods, plates, or screws to reinforce the bone. In some cases, bone cement may be injected into bones, particularly in the spine, to provide stability and reduce pain.
Urgent Medical Issues
Two urgent medical issues require immediate attention. Hypercalcemia, with abnormally high calcium levels, occurs when bone breakdown releases excessive calcium. Symptoms include excessive thirst, frequent urination, nausea, constipation, and confusion. Treatment involves intravenous fluids and medications like bisphosphonates or denosumab to lower calcium levels.
Spinal cord compression, another serious complication, happens when a spinal tumor presses on the spinal cord. Symptoms may include new or worsening back pain, numbness, weakness, or difficulty with bladder and bowel control. Recognizing these symptoms and seeking prompt medical care is important to prevent irreversible neurological damage, as early treatment with corticosteroids, radiation, or surgery can help.