To investigate whether PADI2 expression is important for breast cancer cell proliferation, we next tested whether the pharmacological inhibition of PADI2 activity negatively affects the growth of tumor cells in vitro. We utilized the small molecule inhibitor Cl-amidine for this study because we have previously shown that this drug binds irreversibly to the active site of PADIs, thereby blocking activity in vitro and in vivo[40]. Here, PADI2 is linked to breast cancer.