PARP1 and cancer: Four PARP inhibitors (PARPi) that are blocking the activity of PARP1/2 and are trapping PARP1 on the chromatin have been clinically approved for the treatment of breast (olaparib, talazoparib), ovarian (olaparib, niraparib, rucaparib), prostate (rucaparib), and pancreatic (olaparib) cancer (Kim and Nam, 2022).