Jan. 18 (HealthDay News) -- By studying blood cells in a young pair of twins, scientists say they're gaining new insight into how some children are poised to develop leukemia even before birth.

The researchers report in a new study that both twins -- one who developed leukemia and one who didn't -- shared cells that mutated and became precancerous. In one of the twins, the cancer-ready cells developed enough mutations to sicken the child.

The findings are a "first look at the earliest events in the process that ultimately leads to leukemia," said study co-author Tariq Enver, a professor at John Radcliffe Hospital in Oxford, England.

According to Enver, the next step is to figure out how to use this knowledge to help scientists do a better job of targeting specific leukemia cells with "smart" drugs.

Leukemias can affect both children and adults. An estimated 44,240 cases of the disease were diagnosed in the United States in 2007, according to The Leukemia & Lymphoma Society.

Fortunately, the death rate from leukemia for children has fallen drastically over the past 30 years, although several hundred still die of the disease in the United States each year. The society estimates that 21,790 Americans died of the disease in 2007.

In the new study, published in the Jan. 18 issue of the journal Science, Enver and colleagues in the United Kingdom, Japan and Italy looked at cells in the blood of identical female twins. One developed leukemia at the age of 2, while the other remained healthy.

At issue: Before birth, did the twins share a certain type of cell that became cancerous in one twin but not in the other? The answer, the study found, is yes.

According to Enver, both twins ended up with precancerous cells, which they shared in the uterus by both getting blood from the same placenta. Somehow, further mutations made the precancerous cells become cancerous in the twin who became ill.

Dr. Bart Kamen, chief medical officer of The Leukemia & Lymphoma Society, lauded the study as a "remarkable paper" that provides a new perspective on how leukemia develops. Essentially, he said, the study suggests that the precancerous cells don't always cause cancer but can do so under a specific condition -- that is, if they mutate beyond the initial aberration that made them dangerous in the first place.

As for the implications for treatment, the research suggests that "even if we killed the leukemia by killing the cells that are malignant, this one [cell type] might still be there. Maybe we didn't kill it," Kamen said.

But if scientists can figure out where the precancerous cells are, they can try to destroy them as well, he said.

Evers said the research could allow scientists to figure out which specific cells need to be targeted by drugs and allow doctors to monitor whether a treatment is working properly.

More information:

There's more on leukemia at The Leukemia & Lymphoma Society.

SOURCES: Tariq Enver, Ph.D., professor, MRC Molecular Haematology Unit, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Oxford, U.K.; Bart Kamen, M.D., Ph.D., chief medical officer, The Leukemia & Lymphoma Society, White Plains, N.Y.; Jan. 18, 2008, Science