Slight differences were observed in cancer cells treated with trastuzumab and co-cultured cells treated with trastuzumab in HER2 moderately overexpressing cell line, MDA-MB-453; however, this difference was only trending towards statistical significance, suggesting immune stimulation in trastuzumab treated HER2 + breast cancer cells is related to HER2 expression. The gene discussed is ERBB2; the disease is cancer.