ERBB2 and breast carcinoma: More recently, a detailedChIP-chip study demonstrated that PAD2 also plays a critical rolein ER target gene activation via the citrullination of histone H3Arg26at ER target gene promoters.32 Additionally,it was found that PAD2 expression is highly correlated with HER2 expressionacross more than 60 breast cancer cell lines.30 From a therapeutic standpoint, 75% and 15% of all breast cancersare ER and HER2+, respectively.