MAPK3 and neoplasm: This reduction in tumor size in G415 xenografts was paralleled by the reduction in the amounts of phospho‐ERK1/2 by immunohistochemical analyses (Figs. 4c–4d, lower panel) of explanted tumors, further validating our in vitro findings (Fig. 3a) and implicating ERBB2 as an important therapeutic target under neo‐adjuvant or adjuvant settings in treating gallbladder cancer patients.