NCX1 silencing did not alter proliferation either in JIMT1 (a model of human epidermal growth factor receptor 2 (HER2)-positive breast cancer that possesses an amplification of HER2 receptor, but in which the cells do not respond to HER2 inhibition by trastuzumab, which selectively binds to the extracellular domain of HER2), or in MDA-MB-231 (a triple negative breast tumor-derived cell line). The gene discussed is SLC8A1; the disease is breast cancer.