The expression pattern of certain genes may someday help doctors to diagnose and predict whether or not an individual has an aggressive form of B-cell chronic lymphocytic leukemia (CLL), Jefferson cancer researchers have found. Scientists, led by Carlo Croce, M.D., director of Jefferson’s Kimmel Cancer Center and professor and chair of microbiology and immunology at Jefferson Medical College of Thomas Jefferson University in Philadelphia, looked at the expression of genes that encoded microRNAs (miRNAs), tiny pieces of genetic material that are thought to be important in the regulation of gene expression and in the development of cancer. MiRNAs can serve as stop signs for gene expression and protein synthesis, and are thought to play important roles in regulating gene expression in development.