The specific cause of leukemia is still not known. Scientists suspect that viral, genetic, environmental or immunologic factors may be involved.
People with immune-system deficiencies appear to be at greater risk for cancer because of the body’s decreased ability to resist foreign cells. There is evidence that patients treated for other types of cancer with some types of chemotherapy and/or high-dose radiation therapy may later develop leukemia.
All of these factors may explain why a small number of people develop leukemia. But, among most people, the cause of leukemia is not known.