The ability of E2 to induce mitochondrial-mediated apoptosis in AI-resistant MCF-7:5C cells has previously been reported by our laboratory [11,17]; however, this is the first study to show that suppression of IFITM1 induces p21 and Bax expression and enhances E2-induced cell death in AI-resistant breast cancer cells. The gene discussed is IFITM1; the disease is breast carcinoma.