ERBB2 and breast cancer: However, trastuzumab, pertuzumab, and T-DM1 did not show meaningful benefits in the low HER2-expressing breast cancer population (Burris et al., 2011; Chick et al., 2021; Fehrenbacher et al., 2020; Filho et al., 2021; Gianni et al., 2010; Yazaki et al., 2020).