Breast cancer develops when cells in the breast tissue begin to grow uncontrollably, forming a tumor. This abnormal growth typically starts in the milk ducts or lobules, the glands that produce milk. While many breast lumps are not cancerous, malignant tumors can grow into and damage nearby healthy tissue. This disease may extend beyond its initial site.
The Pathways of Spread
Breast cancer cells can leave the original tumor through several mechanisms. One way is direct invasion, where cancer cells produce enzymes that break down the surrounding extracellular matrix. This allows them to penetrate and infiltrate adjacent healthy breast tissue.
Cancer cells can also enter the body’s circulatory systems. They may migrate into blood vessels surrounding the tumor. Once inside the bloodstream, these cells can travel to distant organs, exit the vessels, and establish new tumor colonies.
The lymphatic system also provides a pathway for spread. Lymphatic vessels are present around tumors, and cancer cells can enter these vessels. These vessels drain into lymph nodes, which function as filtering stations. Cancer cells can become trapped in these nodes, where they may multiply and form new tumors.
Where Breast Cancer Can Spread
When breast cancer spreads beyond the breast and regional lymph nodes, it is referred to as metastatic, or stage 4, breast cancer. The most common distant sites for these new tumors include the bones, lungs, liver, and brain. Even when breast cancer cells spread to these distant organs, the new tumors are still considered breast cancer, not cancer of the affected organ.
Bones are the most frequent site of breast cancer metastasis, affecting a significant percentage of individuals. The spine, ribs, pelvis, and long bones of the arms and legs are commonly affected. Lung metastasis is also common, as blood passes through the lungs. The liver is another common destination for metastatic breast cancer. The brain can also be affected, though less commonly than bones, lungs, or liver. Other less common sites of spread include:
Less Common Sites
Female reproductive tract
Digestive tract
Pancreas
Kidneys
Thyroid
Treatment Approaches for Spread Breast Cancer
Treatments for metastatic breast cancer primarily involve systemic drug therapies aimed at managing the disease and extending survival. These treatments circulate throughout the body to target cancer cells wherever they may have spread. Common systemic therapies include:
Hormone therapy
Chemotherapy
Targeted therapy
Immunotherapy
Hormone Therapy
Hormone therapy is often used for hormone receptor-positive metastatic breast cancer, especially when the disease is not immediately life-threatening. This approach, which can involve medications like aromatase inhibitors or tamoxifen, works by blocking the effects of hormones that fuel cancer cell growth. Patients may receive these therapies as pills or injections, often continuing for several years.
Chemotherapy
Chemotherapy uses powerful drugs to kill rapidly dividing cancer cells throughout the body. While it can be taxing, it is administered in cycles, typically every two to three weeks, with breaks in between to allow the body to recover. It can be used alone or in combination with other treatments, sometimes as a first-line approach for life-threatening disease progression.
Targeted Therapy
Targeted therapies specifically attack certain molecules or pathways involved in cancer cell growth and survival, often with fewer side effects on healthy cells than chemotherapy. For instance, HER2-targeted drugs are used for HER2-positive breast cancer. Newer personalized medicine therapies are also emerging for different breast cancer subtypes.
Immunotherapy
Immunotherapy is a newer approach that harnesses the body’s own immune system to recognize and destroy cancer cells. While systemic therapies are the main treatment for metastatic breast cancer, localized treatments like radiation therapy or surgery may also be used in specific situations to manage symptoms, prevent complications, or achieve local control of the disease.