The binding between trastuzumab and HER2 may be disrupted by the membrane-associated glycoprotein mucin-4 (MUC4), as evidenced by the overexpression of MUC4 in a trastuzumab-resistant breast cancer cell line and subsequent restoration of trastuzumab binding through MUC4 siRNA knockdown [28]. The gene discussed is ERBB2; the disease is breast cancer.