Fatigue is the most common, and one of the most devastating symptoms among patients with cancer. According to the National Comprehensive Cancer Network (NCCN), cancer-related fatigue (CRF) is "a distressing, persistent, subjective sense of physical, emotional, and/or cognitive exhaustion related to cancer or its treatment that is not proportional to recent activity". Fatigue occurs across the spectrum of cancer types and treatments. CRF has a negative impact on all areas of function, including mood, physical function, work performance, social interaction, family care, cognitive performance, schoolwork, and community activities. CRF has been rated as more troublesome and to have a greater negative impact on quality of life than other cancer-related symptoms such as pain, depression, and nausea. CRF can persist for months or years after cancer therapy is completed.