ERBB2 and breast cancer: Given that PAD2 likely plays an importantrole in the biology of both ER and HER2+ lesions, these observationssuggest that PAD2 could represent a therapeutic target for 85–90%of all breast cancers in humans.30 Thehigh-resolution structures of PAD1–4 have been reported.9,33−35 The catalytic activity for PADs is known to be regulatedby calcium ions through conformational changes, including the appropriatepositioning of the catalytic cysteine in the active site cleft.