Stewart-Treves syndrome is a sarcoma (form of cancer) of an arm affected by lymphoedema (hard swelling) in the elderly. The lymphoedema usually follows mastectomy (breast removal) for cancer. A purplish red growth (angiosarcoma) develops on the lymphoedematous limb. The diagnosis is confirmed after surgical removal of the tumour and examination under a microscope. These are relentlessly aggressive tumours with a poor prognosis.