Although trastuzumab treatment against human PDA cells has shown significant antitumor activity in basic in vivo and in vitro studies, the combined treatment of gemcitabine (GEM) or capecitabine with trastuzumab against metastatic PDA did not result in improved progression-free survival or overall survival, possibly because the expression and gene amplification of HER2 in PDAs were generally lower than in breast cancer [14, 15]. This evidence concerns the gene ERBB2 and breast cancer.