Cancer-related fatigue feels very different from everyday fatigue, said Lillian Nail, PhD, RN, a cancer survivor who has studied this side effect at the University of Utah School of Nursing. " ?Overwhelming? is the most common description," said Dr. Nail. "When compared with the fatigue experienced by healthy people, cancer-related fatigue is more severe, it lasts longer, and sleep just doesn?t bring relief."

The causes of cancer-related fatigue are not fully known. Problems like a low blood count, sleep disruption, stress, eating too little, and other factors may contribute to this condition.

A common, frustrating problem About 90 percent of patients experience fatigue during chemotherapy or radiation therapy treatment, added Dr. Nail. For patients receiving cyclic chemotherapy, fatigue often peaks within a few days and declines until the next treatment when the pattern begins again. For patients receiving radiation, fatigue usually increases as the treatment continues. It may last from three months to one year after treatment ends.

For these patients, their personal definition of what is normal changes; being tired becomes the new normal, said Barbara Piper, DNSc, RN, associate professor of nursing at the University of Nebraska. Mental fatigue often results from the intensive mental effort and excessive attention that is necessary when coping with a serious illness. "For example, a woman with newly diagnosed breast cancer must absorb the impact of the diagnosis as well as make treatment decisions to go on with her life," added Piper.

Physicians often don?t prepare patients for this frustrating side-effect of cancer, said Russell Portenoy, MD, chairman of the Department of Pain Medicine and Palliative Care at Beth Israel Medical Center in New York City, and a member of the Fatigue Coalition, a group of medical researchers and practitioners who are making more patients and health care providers aware of this condition. Left untreated, fatigue can upset the patient?s quality of life.

Fatigue or depression? Because some fatigue symptoms seem to mirror those of depression, health care providers often confuse the two, said Dr. Nail. Depression involves an inability to feel pleasure?people who are depressed feel sad, unworthy, despair or guilt. "It?s entirely possible to be fatigued but not depressed," she explained, adding patients sometimes have trouble finding a label for what they?re feeling. They simply know they can be overwhelmed with fatigue at any time, no matter what they are doing.

Some signs of cancer-related fatigue are: - Feeling tired, weary or exhausted even after sleeping - Lacking energy to do your regular activities - Having trouble concentrating, thinking clearly, or remembering - Feeling negative, irritable, impatient, or unmotivated - Lacking interest in normal day-to-day activities - Spending less attention on personal appearance - Spending more time in bed or sleeping

At times, there may be physical causes of fatigue, like infection or pain that disrupts sleep. When those problems are not present, it is possible to combat fatigue, said Dr. Nail. "It?s a matter of identifying the times of day when you have more energy than others," she explained. "It means finding alternative ways of doing things, deciding what you can give up, setting priorities, and then getting help."