To investigate whether the expression of ERBB2 i14e contributes to trastuzumab resistance in other types of cancers, not limited to GBC, we assessed ERBB2 i14e levels in a secondary trastuzumab-resistant breast cancer cell line SKBR344 and found identical results with increased ERBB2 i14e (Fig. 4l, m). Here, ERBB2 is linked to breast cancer.