CERT1 and breast cancer: COL4A3BP expression was also shown to be raised in drug-resistant cell lines and in paclitaxel-resistant ovarian tumours, suggesting that COL4A3BP expression is a cause of drug resistance and a potential target for use in chemotherapy-resistant cancers.21 Bernards and colleagues22 used a large-scale RNAi screen to discover determinants of trastuzumab (Herceptin) resistance in breast cancer.