The specific cause of leukemia is still not known. Scientists suspect that viral, genetic, environmental or immunologic factors may be involved.
- Viruses: Some viruses cause leukemia in animals, but in humans, viruses cause only one rare type of leukemia. Even if a virus is involved, leukemia is not contagious. It cannot spread from one person to another. There is no increased occurrence of leukemia among people such as friends, family and caregivers who have close contact with leukemia patients.
- Genetics: There may be a genetic predisposition to leukemia. There are rare families where people born with chromosome damage may have genes that increase their chances of developing leukemia.
- Environmental factors, such as high-dose radiation and exposure to certain toxic chemicals, have been directly related to leukemia. But this has been true only in extreme cases, such as atomic bomb survivors in Nagasaki and Hiroshima or industrial workers exposed to benzene. Exposure to ordinary x-rays, like chest x-rays, is not believed to be dangerous.
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.