Missing, malformed or damaged lymph vessels or lymph nodes cause a blockage of the lymphatic system. Unable to drain properly, the lymphatic fluid collects in the tissue, and results in swelling. Lymphedema in legs is particularly common, especially due to obesity and treatment for cancer.
After breast cancer surgery, lymphedema most frequently occurs in the arm. As cancer cells spread through the lymph vessels into the lymph nodes first, many patients have at least 1-3 lymph nodes removed from under the arm (sentinel lymph node biopsy) or sometimes even more (axillary lymph node dissection). Radiation therapy is often part of cancer therapy and can destroy the lymphatic system as well. In such cases, compression therapy is often recommended to manage swelling and support lymphatic drainage in the arm.