HER2‐positive gastric cancer cells resistant to trastuzumab emtansine discarded trastuzumab emtansine into the extracellular space by EV secretion (Le Joncour et al., 2019), and since a sufficient intracellular concentration of the cytotoxic payload DM1 is essential for the anti‐cancer activity (Barok et al., 2014), expulsion of DM1 may contribute to trastuzumab emtansine resistance (Figure 4). This evidence concerns the gene ERBB2 and cancer.