It has further been demonstrated that the plasma membranes of cancer cells have unique phospholipid compositions that include a particular enrichment of externalized PS on the outer leaflet, which is enhanced under conditions of oxidative stress (167, 168); interestingly, exposure of PS on the surface of CTLs has been shown to trap perforin in a dysfunctional, non-pore-forming conformation and it has been speculated that the enrichment of PS on the tumor cell membrane may provide enhanced protection against perforin (169). Here, PRF1 is linked to cancer.