Even in the presence of a properly signaling TNF receptor signaling pathway that involves FADD and TRADD, breast cancer cells do not undergo apoptosis in response to TNF-alpha, allowing tumors to grow and metastasize. A close inspection shows that one protein is no longer expressed in these cells. The addition of TNF-alpha leads to TRADD and FADD complexes but does not lead to cell death. Procaspase 3 is expressed and functioning. A western blotting analysis shows that NFkB is expressed, and other studies show that the protein is functioning properly in these cells. What is the most likely cause of resistance to cell death by TNF-alpha in breast cancer cells