Narrator: This is Science Today. Each year, about 25 hundred children in this country are diagnosed with acute lymphoblastic leukemia. Joseph Wiemels, (Wee-mills) a research molecular epidemiologist at the University of California, San Francisco, says this is the most common form of childhood leukemia and it's on the rise. The goal now, is to understand why.

Wiemels: From understanding comes prevention. Childhood leukemia is a very curable disease, it's curable in seventy percent of cases, but there are actually costs from the cure itself. The chemotherapy can cause developmental abnormalities or secondary cancers later in life, so the best thing to do is prevent it.

Narrator: Wiemels and his colleagues discovered evidence suggesting there are two genetic changes that cause this form of leukemia - one occurring in the womb, and the other mutation formed in early childhood, due to environmental factors.

Wiemels: We believe that those environmental factors have to do with an aberrant response to common infections and we believe that those infections are the cause of the second mutation.

Narrator: For Science Today, I'm Larissa Branin.