ERBB2 and breast cancer: To test whether PADI2 displays a restricted expression pattern with respect to breast cancer subtype, we next investigated PADI2 mRNA and protein expression in cell lines representing four common breast cancer subtypes: MCF7 (luminal A), BT-474 (luminal B), SK-BR-3 (HER2/ERBB2+), and MDA-MB-231 (basal).