Cancer is characterized by uncontrolled cell growth and occurs when programmed cell death breaks down. Unlike regular cells, cancer cells do not die and instead continue growing and dividing uncontrollably. While some cancers cause obvious symptoms as they grow and spread, others may not cause symptoms until they are quite large. Research suggests that lifestyle choices like diet, physical activity and smoking account for about half of cancer cases, making many cancers preventable. Common cancers include bladder, breast, lung, prostate, leukemia and kidney cancer.