U.S. doctors are using a new technique to determine which children suffering from an acute form of leukemia are likely to have a relapse after treatment.

In a report published on Friday in The Lancet, a British medical journal, doctors at St. Jude Children's Hospital in Memphis, Tennessee, described how the tech-nique, called multiparameter flow cytometry, can help them predict which patients with acute lymphoblastic leukemia (ALL) will relapse by detecting leftover cancer cells in their bone marrow.The instrument can find one leukemic cell among 10,000 normal cells, compared to conventional methods which can detect only one cancerous cell in 100 healthy ones.

Patients with detectable residual cancer cells are four to nine times more likely to relapse.

"This study shows that residual leukemia, undetectable by conventional methods, strongly predicts relapse in children with ALL if found at any point in the patient's treatment," Dr. Dario Campana said in a statement.

"With this new understanding of the relationship between residual disease and relapse, and the resulting changes in the way ALL patients are treated, we can take another step in improving the cure rate for ALL," he added.

Acute lymphoblastic leukemia is the most common form of childhood cancer. Nearly a quarter of children treated will have a relapse and most of them will die from the disease.

The researchers followed 158 children newly diagnosed with the disease. All the youngsters were in remission after six weeks of chemotherapy treatment and were continuing with consolidation therapy when the researchers took bone marrow samples at weeks 14, 32, and 56 and at the end of treatment at 120 weeks.

The doctors used probes, called antibodies, coupled with fluorescent dyes to specifically tag leukemia cells. Levels of leukemia were calculated using the flow cytometer, which detects signals from the dyes and counts the numbers of cancer cells.

"These tests redefine remission; our study shows that they also give physicians information about the likelihood of treatment success," Campana added.

A higher degree of marrow infiltration by leukemia cells in week 14 samples indicated a subset of patients with a particularly poor prognosis.

Although there is no cure for the disease, thanks to advances in treatments more than 75 percent of children with ALL survive.