The immune system plays a fundamental role in identifying and eliminating abnormal cells that may contribute to cancer development. Although cancer prevention cannot be guaranteed through immune enhancement alone, substantial scientific evidence indicates that immune competence influences cancer risk. Lifestyle-related factors such as nutrition, physical activity, sleep quality, and stress regulation affect immune surveillance and inflammatory balance. Understanding these relationships allows individuals to adopt evidence-based behaviors that may support immune health and reduce long-term cancer risk. 1. Immune Surveillance and Cancer Biology The concept of immune surveillance describes the immune system’s capacity to detect and eliminate emerging malignant cells before they proliferate. Key immune components, including cytotoxic T lymphocytes and natural killer (NK) cells, are involved in recognizing tumor-associated antigens and initiating targeted immune responses. Impairment of immune surveillance has been associated with increased cancer incidence, particularly in immunocompromised populations. According to the National Cancer Institute (NCI), reduced immune function may allow mutated cells to evade detection, increasing the likelihood of tumor initiation and progression. A tumor forms when normal cells undergo genetic mutations that disrupt the usual controls on cell growth, division, and programmed cell death (apoptosis). These mutations may arise from DNA replication errors, exposure to carcinogens, chronic inflammation, or inherited genetic factors. As regulatory mechanisms fail, affected cells begin to divide uncontrollably and evade immune surveillance, leading to the accumulation of abnormal cells. Over time, these cells may acquire additional mutations that promote sustained growth, resistance to cell death, and the ability to stimulate new blood vessel formation, resulting in a mass of tissue known as a tumor.