Importantly, cancer susceptibility occurs at especially high incidence (10–15%) of lymphoproliferative disorders in childhood or early adulthood.37 In addition to CLL, the region on chromosome 11 containing the ATM gene is frequently deleted in Mantle cell lymphoma and T-cell prolymphocytic leukemia.38 Deletion of 11q has been recognized as a poor prognostic factor for CLL in progression-free survival and overall patient survival.2 Several studies have been conducted to test the clinical significance of ATM mutations in different cohorts of CLL patients. This evidence concerns the gene ATM and T-cell prolymphocytic leukemia.