FASLG and cancer: Furthermore, upregulation of FasL in cancer cells may worsen the prognosis by causing ‘counterattack’ against natural killer (NK) cells and tumor infiltrating lymphocytes (TILs) which are responsible as antitumor effector cells (Chappell and Restifo, 1998; Igney et al., 2000; O’connell et al., 1996).