The ATM-Chk2-p53 signaling axis plays an important role in regulation of apoptotic response to DNA damage in CLL, as mutations in ATM and TP53 are enriched in patients with secondary resistance to DNA-damaging chemotherapy (Bartkova et al., 2005; Landau et al., 2013). This evidence concerns the gene CHEK2 and B-cell chronic lymphocytic leukemia.