Accumulated Tregs in tumor microenvironment suppress immune response against tumor cells by inducing apoptosis of T cells through secretion of perforin and granzyme, inhibiting maturation of antigen presenting cells (APCs) via cytotoxic T lymphocyte antigen-4 (CTLA-4) and lymphocyte-activation gene 3 (LAG3), or producing immune suppressive cytokines such as IL-10 [7]. Here, PRF1 is linked to neoplasm.