PARP1 and breast cancer: Overexpression and activation of CASP7 in BC cell lines underlined the possible activation processes facilitated by initiator caspases, CASP8 and CASP9.62 The cleavage of poly-(ADP-ribose) polymerase 1, hallmark of CASP3/CASP7 activation63 was not detected despite the presence of activated CASP8 and CASP7 in the BC cells (data not shown).