Cancer is a group of diseases characterized by the uncontrolled growth and spread of abnormal cells that can invade surrounding tissues and, in some cases, metastasize to distant parts of the body. It develops when genetic mutations disrupt normal cell regulation, allowing cells to multiply without proper control or programmed cell death. There are many types of cancer, including carcinomas, sarcomas, leukemias, lymphomas, and brain tumors, each affecting different tissues or organs. Symptoms vary widely depending on the location and stage but may include unexplained weight loss, fatigue, persistent pain, lumps, changes in skin or bowel habits, or abnormal bleeding. Risk factors include genetics, tobacco use, radiation exposure, certain infections, environmental toxins, and lifestyle factors. Early detection through screening and timely treatment—such as surgery, chemotherapy, radiation, immunotherapy, or targeted therapy—can significantly improve outcomes.