Introduction Tumor suppressor genes represent one of the most important cellular defense mechanisms against cancer development. These genes function to regulate cell growth and division, repair DNA damage, and prevent abnormal cellular proliferation. When these genes function properly, they maintain cellular stability and protect the body from the transformation of normal cells into cancerous ones. Functions of Tumor Suppressor Genes Tumor suppressor genes perform several essential roles, including: Controlling the cell cycle and preventing uncontrolled cell division Repairing DNA damage that occurs during replication Inducing programmed cell death (apoptosis) when damage cannot be repaired Loss or mutation of these genes disrupts cellular control systems, increasing the likelihood of tumor formation. Examples of Tumor Suppressor Genes Among the most well-known tumor suppressor genes are: TP53: Known as the “guardian of the genome,” responsible for halting cell division and repairing DNA damage RB1: Regulates progression through the cell cycle BRCA1 and BRCA2: Play key roles in DNA repair; their mutations are associated with breast and ovarian cancers From Normal Cell to Cancer Cell For tumor suppressor genes, cancer often develops when both copies of the gene are inactivated — a concept known as the two-hit hypothesis. This complete loss of function removes growth control mechanisms, allowing malignant transformation to occur. Medical and Research Significance Understanding tumor suppressor genes is essential for: Early cancer diagnosis and risk prediction Development of targeted cancer therapies Genetic counseling and preventive strategies Conclusion Tumor suppressor genes act as molecular safeguards that protect cells from malignant transformation. Their inactivation plays a central role in carcinogenesis, making them a critical focus in modern oncology research and therapeutic development. AL_mustaqbal University is the first university in Iraq