Final answer:
Cancer is the disease caused by the breakdown in a cell's ability to regulate its own division, leading to uncontrolled cell growth and the potential formation of tumors or leukemia.
Step-by-step explanation:
The disease that results from a breakdown in a cell's ability to regulate its own division is cancer. This loss of control begins with a change in the DNA sequence of a gene responsible for regulating the cell cycle. Faulty instructions from these genes lead to proteins that do not function correctly, which causes a disruption in the cell’s monitoring system. This disruption allows mistakes to be passed on to daughter cells, leading to more accumulated damage with each cell division. Eventually, all checkpoints become nonfunctional, causing the unregulated and rapid cell division that characterizes cancer. These rapidly dividing cells can form tumors or, in the case of blood cancer, leukemia.