Cancer-related fatigue is a symptom of fatigue that is experienced by nearly all cancer patients. Among patients receiving cancer treatment other than surgery, it is essentially universal. Fatigue is a normal and expected side effect of most forms of chemotherapy, radiation therapy, and biotherapy. On average, cancer-related fatigue is "more severe, more distressing, and less likely to be relieved by rest" than fatigue experienced by healthy people. It can range from mild to severe, and may be either temporary or a long-term effect. Fatigue may be a symptom of the cancer, or it may be the result of treatments for the cancer. Pathophysiology The pathophysiology of cancer-related fatigue is poorly understood. It may be caused by the cancer or the effects it has on the body, by the body's response to the cancer, or by the cancer treatments. Fatigue is a common symptom of cancer. Some fatigue is caused by cancer treatments. This may show a characteristic pattern. For example, people on many chemotherapy regimens often feel more fatigue in the week after treatments, and less fatigue as they recover from that round of medications. People receiving radiation therapy, by contrast, often find their fatigue steadily increases until the end of treatment. Proposed mechanisms by which cancer can cause fatigue include an increase in pro-inflammatory cytokines, dysregulation of the hypothalamic-pituitary-adrenal axis, disruption of circadian rhythms, muscle loss and cancer wasting, and genetic problems. Additionally, some forms of cancer may cause fatigue through more direct mechanisms, such as a leukemia that causes anemia by preventing the bone marrow from producing blood cells efficiently. A relationship between Interleukin 6 and fatigue has been observed in studies, albeit inconsistently. Increased markers of sympathetic nervous system activity are also associated with cancer related fatigue. Screening The National Comprehensive Cancer Network recommends that every cancer patient be systematically screened for fatigue at the first visit with an oncologist, throughout treatment, and afterwards. Screening typically involves a simple question, like "On a scale of one to ten, how tired have you felt during the last week?" More detailed information may be collected in a symptom journal. Diagnosis Some causes of cancer-related fatigue are treatable, and evaluation is directed towards identifying these treatable causes. Treatable causes of cancer-related fatigue include: anemia, pain, emotional distress, sleep disturbances, nutritional disturbances, decreased physical fitness and activity, side effects from medications (e.g., sedatives), abuse of alcohol or other substances. Additionally, other