ERBB2 and breast cancer: Adotrastuzumab emtansine (Kadcyla®) against HER2, approved for solid cancers such as breast cancer in February 2013, entered the cell via RME and released lysine-MCC-DM1 (Figure 4) as a catabolite to the cytoplasm through carrier-mediated transport using the lysosomal transporter SLC46A3 [54] in the lysosomal escape process [24].