For example, while over-expressed by 15–20% of breast cancers, HER2 is also expressed by gastrointestinal, respiratory, reproductive, and urinary tract cells as well as in the skin, breast and placenta.127 Its expression on cardiomyocytes is thought to be the underlying pathogenic mechanism of cardiac side effects seen in patients treated with the anti-HER2 antibody trastuzumab.128. This evidence concerns the gene ERBB2 and breast carcinoma.