Fatigue is one of the most common symptoms experienced by cancer patients during and after treatment. Common causes of fatigue include the effects of cancer on the body; treatments such as radiation therapy, chemotherapy, and surgery; other medical conditions; or emotional problems such as anxiety or depression. Psychiatrist William Breitbart, MD of Memorial Sloan-Kettering Cancer Center explains what cancer-related fatigue is, its effects, and ways to fight cancer-related fatigue.