Lymphoedema is the accumulation of excessive amounts of fluid in the tissues (interstitium) leading to chronic swelling in one or more regions of the body due to a blockage or defect in the lymphatic system. 

 This chronic inflammatory process is progressive and involves increased levels of proteins in the interstitial space (outside the cells) and subsequent abnormal cellular behaviour leading to free fluid accumulation, fibrosis and fatty tissue development.​

Around one in five breast cancer patients will develop lymphoedema as a potential side effect post mastectomy or post radiation therapy. The condition can present whilst undergoing treatment or within the years following treatment. 

For patients who have been treated for breast cancer, the condition usually occurs in the hand and arm but can also affect the breast, underarm, chest, trunk, and/ or back.