In the present study, we have demonstrated that interferon signaling is dysregulated in AI-resistant breast cancer cells and AI-resistant/recurrence tumors and that several interferon response genes including; IFITM1, PLSCR1, STAT1, STAT2, IRF-7, IRF-9, IFIT1, OAS1 and MX1 are constitutively overexpressed in AI-resistant breast cancer cells. The gene discussed is IRF9; the disease is breast carcinoma.