Wnt3A, FZD6, and CTNNB1 were upregulated, whereas GSK-3β was downregulated in trastuzumab-resistant GC cell lines compared to their parental cells, suggesting that the acquirement of trastuzumab resistance was closely associated with the activation of Wnt/β-catenin signaling in GC. Here, WNT3A is linked to gastric cancer.