Childhood leukemia is rare, with approximately 2,500 cases diagnosed in the U.S. every year. But parents of these children are haunted by this question: "Why did my child get leukemia?" Below, two thought leaders in leukemia research and treatment shed some light on this condition, and this difficult question.

Q: What is childhood leukemia?
CLAUDIO SANDOVAL, MD: As in adults, leukemia in children is characterized by an overproduction of an abnormal group of cells that then repopulate the bone marrow which is responsible for producing red blood cells (carry oxygen), white blood cells (fight infections), and platelets (prevent bleeding). In repopulating the marrow, they also inhibit normal blood cells from being produced. These children don't have normal white blood cells that fight infection, so they are at an increased risk for developing life-threatening infections. And they don't produce red blood cells, so they become anemic.

Q: The white blood cells are diseased?
CLAUDIO SANDOVAL, MD: Yes. These are diseased white blood cells that, due to their inability to mature, can't do their job correctly. It's almost like asking an infant to run. When he becomes a toddler, he will run, but as an infant he cannot. So these white blood cells are essentially infants. And they never get to the toddler stage. For whatever reason, they just can't understand the normal messages in the body that tells them to mature.

Q: What are the symptoms of leukemia in children?
CLAUDIO SANDOVAL, MD: When the children are anemic, they are not as active; They are not as playful, they don't eat as much, and they start becoming pale. Since they don't produce platelets-which help the body from losing blood-so these children can have bloody noses, bleeding gums, and bruises all over their bodies. And those three symptoms alert the parents that something is going on, that something is not right with their child.

Q: A lot of parents whose children are diagnosed struggle with the reason why their children have leukemia. What would you tell these parents?
SHARON P. MAYER: I think the most important message for parents is that It's not their fault. There can be genetic factors that come from numerous places. You also have environmental factors that all come together in just the right way to cause this very rare event. You could have a brother and a sister, both exposed to similar things, and yet only one develops leukemia. One of their cells was altered somehow, so that when it divided, its progeny cells carried that mutation with it and then from there it had other mutations down the line that caused the leukemia.

Q: Are there some children who are more susceptible to this disease than others?
CLAUDIO SANDOVAL, MD: There are some children who have an increased risk for leukemia, such as are those with Down Syndrome. Children with Down Syndrome have an extra chromosome 21. In some children who don't have Down Syndrome, their leukemia cells have an extra chromosome 21. So it might be possible that there is a gene on chromosome 21 that the child with Down Syndrome is getting an extra dosage of.

There are children with very rare immunodeficiency disorders such as Wiskott-Aldrich Syndrome, or Duncan's Syndrome who are at an increased risk for developing lymphoid malignancies, lymphomas and leukemias. Even though these patients are very, very rare -- it's even rarer than the leukemia itself -- they teach us very important lessons about the immunology of leukemia. Why does this patient with this very rare immune deficiency syndrome develop leukemia? Because his immune system doesn't function properly. So if you take all these rare children with immunodeficiencies and you group them together as a whole, you have a relatively large number of patients. When you piece together their immunodeficiencies, you realize that their immunodeficiencies shed some light on the importance of the normal immune response.

We learn from our patients. I always teach medical students and residents that your best teacher is not the textbook, it's not your professor, but it's your patient. Know your patient. Talk to your patient. See a lot of patients. This way you see how a disease presents in different phases.

Q: How early does leukemia start developing in the body?
SHARON P. MAYER: There is evidence that suggests that this coalescing of multiple factors can start as early as in utero. A group of people in England published a very interesting study in which they looked at specific genetic rearrangements, genetic abnormalities in a set of twins who had leukemia. One of the twins was diagnosed at nine, the other at fourteen. Amazingly, these twins had the same genetic abnormality that could not have happened by chance. There was a blood sample from these children at birth, and they found that the same genetic abnormality was present, which shows fairly clearly that these patients had some type of premalignant cell at birth. It may not have been the actual leukemia cell, but some type of cell that was prone to evolve into a malignancy later on, possibly due to an immune deficiency.

Conclusion
For parents, there are a number of important parting messages. Right now there is no way to accurately predict or prevent leukemia. If your child gets it, the most important thing is to not to blame yourself, but to get the child treatment, and to remember that childhood leukemia is, and can be, successfully treated.