[4] As autocrine or paracrine growth factors increase, they may bypass the need for ER-mediated growth stimulation in human breast cancer cells, making anti-hormonal therapy ineffective. Because tamoxifen has also been shown to induce apoptosis in breast cancer cells, failure to undergo apoptosis in response to tamoxifen could confer tamoxifen resistance. [5]. The gene discussed is ESR1; the disease is breast carcinoma.