We have previously established two trastuzumab-resistant cell lines (BT474R and NCI-N87R) respectively derived from HER2-overexpressing breast and gastric cancer cell lines (BT474 and NCI-N87) in vitro by continuously culturing parental cells with increasing dose of trastuzumab for a long period of time and found that these two resistant cells displayed a markedly enhanced phosphorylation of signal transducer and activator of transcription-3 (STAT3) compared to parental cells (unpublished data). The gene discussed is STAT3; the disease is gastric cancer.