The Fas ligand is a trimeric, extracellular protein that binds to its receptor, Fas. The binding of Fas ligand to its receptor alters the conformation of Fas so that it binds an adaptor protein and activates caspase-8. One important role of Fas is to eliminate tumor cells by lymphocytes of the immune system. After studying 35 primary lung and colon tumors, over half were found to have amplified and overexpressed a gene for a secreted protein that binds to the Fas ligand. Explain how the overexpression of this secreted protein might contribute to the survival of these tumor cells. In terms of its structure (below) and function, what molecule is Fas ligand similar to?