Generation of energy in cells depends on aerobic glycolysis and the TCA cycle in mitochondria. Carcinogenesis may start with mutations but the main driver is inadequate energy production. Many internal and external factors can disrupt energy production, especially free radicals, viruses, excess fat, protein, carbohydrates, inadequate oxygen and nutrition which can continuously inhibit or lower energy generation and stimulate immune cells to begin fighting in the area, though cells refuse to die.