CD8+ effector T cells (cytotoxic T lymphocytes, CTLs) serve as key mediators of antitumor immunity by recognizing tumor cells through MHC class I molecules and inducing apoptosis through the release of perforin‐1 (PRF1), granzyme B (GZMB), and IFN‐γ. The gene discussed is CD8A; the disease is neoplasm.