PRF1 and cancer: NK cells without chimeric antigen receptors can kill cancer cells directly by releasing Perforin-1 and Granzyme or by death receptors, or by secreting cytokines and chemokines to activate immune cells such as T cells and B cells, and can also kill cancer cells by antibody dependent cell-mediated cytotoxicity (ADCC), which can better fight against tumor heterogeneity [143].