The lymphatic system helps the body fight infection. It's made up of a network of small vessels located all over the body. Lymph fluid travels through these vessels. Many tiny organs called lymph nodes are scattered along the vessels. These nodes filter lymph fluid to help fight infection.
During surgery for cancer, nearby lymph nodes are often removed. Sometimes radiation therapy is used to treat nearby lymph nodes as part of cancer treatment. This is because cancer cells can break away from the first tumor, get into the lymph vessels, and collect and grow in lymph nodes. This is one of the ways cancer can start to spread (metastasize) to other parts of your body.
Surgery and radiation both disrupt the lymph network. Lymph fluid can't flow the way it should, which can lead to fluid buildup and swelling in soft body tissues. This is lymphedema. The part of the body with lymphedema depends on what area was treated. For instance, treating lymph nodes in the groin can cause lymphedema in the genitals and leg. Damaging underarm or chest nodes can cause lymphedema in the neck, chest, arm pit, and arm on the affected side. When the lymph nodes are treated for head and neck cancers, it can lead to swelling in the face and neck. Swelling can get worse over time and become severe. Skin sores, infections, or other problems can develop.