Pertuzumab does indeed interfere with ligand-induced HER2-HER3 signaling, consistent with its structure-based mechanism of action (Figure S1A; Agus et al., 2002; Sakai et al., 2007), but neither trastuzumab or pertuzumab are effective at disrupting constitutive HER2 signaling in HER2-amplified cancer cells (Figure S1B). This evidence concerns the gene ERBB3 and cancer.