PARP1 and squamous cell carcinoma: Moreover, poly (ADP-ribose) polymerase 1 (PARP1) excision, which together with caspase activation constitutes a hallmark of both intrinsic and extrinsic apoptosis, was detected in p53-deficient FaDu cells (squamous cell carcinoma) treated with EpoB [52] and in RKO cells (p53+) treated with UTD1 [54].