IRF9 and breast carcinoma: Initially, we evaluated the expression of IFN-signaling proteins (STAT1 (Y701), STAT1, STAT2, IRF9) and IFN-stimulated proteins that induce an antiviral state (OAS1 and MxA) in MCF7/pS, MCF7/pR, 231/pS and 231/pR breast cancer cells in the absence or presence of palbociclib.