Using the HER2-amplified BT474 breast cancer cell line, both Trastuzumab-sensitive (Parental) and Trastuzumab-resistant (Resistant) cells were treated with increasing doses of Trastuzumab, SAH5-EJ1, or SAH5-CP, beginning with 2.5 μg/mL (Trastuzumab) or 2.5 μM (peptides), respectively. This evidence concerns the gene CP and breast cancer.