In conclusion, the newly designed ATM-p53 RT-MLPA assay is able to distinguish three subgroups of CLL tumors (i.e., TP53-defective, ATM-defective and WT) and was also able to detect additional samples with a functional defective DDR, without molecular defects of TP53 and/or ATM. This indicates that the ATM-p53 RT-MLPA might not only be of additional clinical value over FISH to screen for mutations of TP53 and ATM instead of sequencing, but might also be useful for screening of other defects in the DDR pathway in addition to ATM and/or TP53 aberrations. Here, TP53 is linked to B-cell chronic lymphocytic leukemia.