Cancer is uncontrolled cell growth that can spread to other parts of the body. It is caused by both external factors like tobacco and chemicals as well as internal factors such as genetic mutations. There are several types of cancer defined by the tissues affected. Common types are carcinomas of epithelial tissue, sarcomas of connective tissue, lymphomas of lymph tissue, and leukemias of blood cells. Cancer develops through a multi-step process as mutations accumulate in genes regulating cell growth. Diagnosis involves examining cells and tissues for abnormalities. Treatment includes chemotherapy with various anti-cancer drugs and radiotherapy to damage cancer cell DNA.