Clinical meaning
Cancer is a group of diseases characterized by uncontrolled proliferation of abnormal cells that have the ability to invade surrounding tissues and metastasize to distant sites. Normal cell growth is tightly regulated by proto-oncogenes (genes that promote cell growth), tumor suppressor genes (genes that inhibit cell growth), and apoptosis (programmed cell death). Cancer develops when mutations accumulate in these regulatory genes, transforming a proto-oncogene into an oncogene (permanently activated growth signal) or inactivating tumor suppressor genes (removing growth brakes). The most well-known tumor suppressor gene is p53, which is mutated in approximately 50 percent of all human cancers. The cell cycle consists of four phases: G1 (cell growth), S (DNA synthesis), G2 (preparation for division), and M (mitosis). Chemotherapy agents target cells at different phases of this cycle; understanding this is essential for safe drug administration. Cancer cells differ from normal cells in several key ways: they ignore growth-inhibiting signals, produce their own growth factors, avoid apoptosis, develop unlimited replicative potential (telomerase activation), induce angiogenesis (new blood vessel formation to supply the tumor), and acquire the ability to invade and...