ATM and B-cell chronic lymphocytic leukemia: The TP53 pathway has been extensively studied in CLL, and chromosomal aberrations such as deletion of 17p13 are known to cause loss of TP53 function.45 In addition, decreased TP53 expression and activity independent of 17p13 deletions have been associated with deletion of the ATM gene, which increases MDM2 activity and in turn leads to decreased TP53 pathway activity 45, 46.