Western blot analysis showing levels of pADPr attached to the PARP1 protein (PARP-pADPr) as an indication of PARP1 activity after 5 Gy IR. (A) Apoptosis-proficient ALL tumors showed pADPr degradation by 8 hours after IR. (B) Apoptosis-resistant ALL tumors showed an absence of pADPr degradation up to 24 hours after IR. (C) Chromatogram of the PARP1 gene sequence in ALL 20. Forward and reverse primer sequencing identified a heterozygous missense 2850G>A mutation in the tumor DNA. The arrow indicates the position of the mutated nucleotide.