Pathophysiology
Clinical meaning
Cancer develops through a multi-step process of genetic mutations that transform normal cells into malignant cells capable of uncontrolled proliferation, tissue invasion, and metastasis. Oncogenes (activated proto-oncogenes such as HER2, RAS, MYC) drive cell proliferation, while tumor suppressor gene inactivation (p53, BRCA1/2, Rb) removes growth regulatory checkpoints. The hallmarks of cancer include sustaining proliferative signaling, evading growth suppressors, resisting cell death, enabling replicative immortality through telomerase activation, inducing angiogenesis via VEGF, and activating invasion and metastasis. Cancer staging using the TNM system (Tumor size, Node involvement, Metastasis) guides treatment planning and prognosis assessment.