TNFRSF1A and cancer: Because normal cells, as opposed to cancer cells, express relatively high levels of MHC class I molecules and low levels of KAR ligands [50, 51], and do not express the major proapoptotic TNF family receptors TNFR1, TRAILR1 and TRAILR2 [52], these two cytotoxic mechanisms mediate selective killing of tumor cells without harming normal cells.