MONDAY, March 12 (HealthDay News) -- Children with the most common type of leukemia now have a dramatically better chance of survival, a new study shows.

The researchers found five-year survival rates among children with acute lymphoblastic leukemia (ALL) increased from about 84 percent to 90 percent from 1990 to 2005. Surviving for five years is considered a cure because so few deaths occur past that timeframe.

"We're talking about a disease that was incurable 50 years ago," said study author Dr. Stephen Hunger. "Now we see a 90 percent cure rate. That's pretty remarkable."

The study is published in the March 12 online issue of the Journal of Clinical Oncology.

Hunger, a professor of pediatrics at the University of Colorado School of Medicine and director of the Center for Cancer and Blood Disorders at Children's Hospital Colorado, said the clinical trials have helped doctors refine their use and dosage of drugs, resulting in greater survival rates. For example, one type of corticosteroid was found to be more effective than another drug in the same class, he said.

ALL is a rare blood or bone-marrow cancer, but it still is the most common form of childhood leukemia. Between 2,800 and 3,000 new cases are diagnosed every year in the United States, Hunger said.

Leukemia, the most common childhood cancer, occurs when the body produces too many abnormal white blood cells, resulting in harm to the immune system and symptoms such as bruising, frequent infections and diarrhea. The acute form progresses quickly if not treated with chemotherapy.

The cause of ALL is not known, but risk factors include having a sibling with leukemia or having had chemotherapy or radiation treatment for some other condition.

The study, done at the University of Colorado, found that the increased survival rate held for all racial and ethnic groups, both sexes, and for all age groups except infants younger than 1 year old. Survival rates improved as the study proceeded.

Death rates fell between 30 percent and 50 percent during the study period, except for among infants, according to the research. Infant survival rates stayed about the same because improvements in drug usage were offset by more deaths from infections and side effects, the study found.

More than 21,000 children with ALL -- more than half of all cases in the United States -- from age 0 to 22, were included in the research. Participants came from the Children's Oncology Group clinical trials funded by the U.S. National Cancer Institute.

Another expert noted that the study shows just how much progress has been made.

"It's amazing, really, that even not knowing why the disease occurs, we can do so well at curing it," said Dr. Arlene Redner, associate chief of oncology in the division of pediatric hematology, oncology and stem-cell transplantation at Cohen Children's Medical Center in New Hyde Park, N.Y.

The study is also important because it shows that effective treatment is widely available, Redner said.

"One of the important things about this study is that it shows that children anywhere in the United States can get this therapy," she said. "It's not just at national treatment centers, but also at small centers."

The future for children with leukemia continues to brighten, Hunger said.

"It's fantastic that now 90 percent of patients can expect to be cured," he said. "However, if your child is part of the 10 percent that isn't cured, it is small consolation."

Efforts now need to focus on that 10 percent, he said, adding: "The goal is to cure everyone."

More information

To learn more about childhood leukemia, visit the Nemours Foundation.