Overexpression of NNMT in breast cancer cell lines SK-BR-3 (ER−, HER2+) and MCF7 (ER+, HER2−), which constitutively do not express NNMT, significantly inhibited doxorubicin (adriamycin)- and paclitaxel-mediated apoptotic cell death and suppression of colony formation. The gene discussed is ERBB2; the disease is breast cancer.