PARP1 and breast cancer: The highlights of the investigation include a demonstration of biological relevancies for PARP1 and PARP2 expression in CRC; the association of low LST status with PARPi response in CRC, in contrast to the established relationship between LST and PARPi response in prostate, pancreatic, ovarian and breast cancers; and the identification of potential, alternative PARPi response biomarkers with non-inferior performances relative to LST status.