PERP and breast cancer: Importantly, we observed that PERP, ITB1, GNAS2, and GNA13 are upregulated by trastuzumab in ErbB2-positive human breast cancer cells BT-474 and MCF-7/Her2-18 (Figs. 2, 3, and 4) which indicates that the effect of trastuzumab on these proteins is not unique to one cell line.