PRF1 and cancer: The TIL subsets are directly cytotoxic to cancer cells via intracellular cytotoxic granules, containing perforin and granzymes, and are also able to indirectly initiate anti-tumor immune responses by secreting various proinflammatory cytokines such as interferon (IFN)-γ, tumor necrosis factor (TNF)-α, and interleukin (IL)-17 [3, 4].