Breast cancer radiation therapy increases the risk of the cancer spreading to organs and bones.
Radiation therapy damages the surrounding healthy tissue. Because radiation therapy is the highest form of high-energy radiation, it damages healthy cells that are located near the cancerous cells. This damage causes the cancer cells to spread to these nearby healthy cells, leading to the cancer spreading to other parts of the body.
Systemic effects of radiation therapy include the release of chemicals and proteins that cause the cancer to spread further. These chemicals and proteins cause the cancer to spread to organs and bones that are not close to the area that was initially affected by radiation including the brain, lungs, bones, and liver.
Radiation therapy can also cause cancer to spread to the lymph nodes, which are small organs located near the breast that help to filter out impurities in the body. Once cancer has spread to the lymph nodes, it can travel to other parts of the body through the lymphatic system.