CD8+ T lymphocytes play an essential role in defense against cancers through recognition by T-cell receptors (TCR) of specific antigenic peptides presented on the surface of malignant cells by major histocompatibility complex class I (MHC-I) molecules, and elimination of the tumor target, mainly by releasing the content of cytolytic granules containing perforin and granzymes. The gene discussed is CD8A; the disease is cancer.