St. Jude Children's Research Hospital scientists said the series of genetic mutations work together to initiate most cases of the often-fatal ALL. The finding, they said, could lead to new cancer-fighting therapies

The defects -- known as "cooperating oncogenic lesions" -- include the deletion of a gene, IKZF1, whose protein, Ikaros, normally helps guide the development of a blood stem cell into a lymphocyte. The researchers also found that loss of the same gene accompanied the transformation of chronic myelogenous leukemias to a life-threatening acute stage.

"These findings provide new avenues to pursue to gain a better understanding of these disease processes and, ultimately, to develop better therapies," said Dr. James Downing, St. Jude's scientific director.

He said the study adds further support to a key concept in cancer genetics -- that malignancies frequently require mutations in multiple genes in order to develop.

The research is reported in the online edition of the journal Nature.