Emergence of Genetic Instability in Children Treated for Leukemia

T cells from patients who had received chemotherapy for B-lineage acute lymphocytic leukemia were studied to determine whether genetic instability, a principal characteristic of cancer cells, can also occur in nonmalignant cells. Consistent with expectations for a genetic instability phenotype, multiple mutations were detected in the hypoxanthine-guanine phosphoribosyltransferase ( HPRT ) reporter gene in independently isolated mutant T cells expressing identical rearranged T cell receptor β (TCRβ) gene hypervariable regions. These results indicate that cancer treatment can lead to genetic instability in nonmalignant cells in some individuals. They also suggest a mechanistic paradigm for the induction of second malignancies and drug resistance.