Final answer:
Cancer is the result of unchecked cell division caused by a breakdown of cell cycle regulation. Faulty instructions in genes lead to proteins that do not function correctly, allowing mistakes to be passed on to daughter cells. Accumulated damage from successive cell divisions can result in the formation of tumors or leukemia.
Step-by-step explanation:
Cancer is the result of unchecked cell division caused by a breakdown of the mechanisms that regulate the cell cycle. The loss of control begins with a change in the DNA sequence of a gene that codes for one of the regulatory molecules. Faulty instructions lead to a protein that does not function as it should. Any disruption of the monitoring system can allow other mistakes to be passed on to the daughter cells. Each successive cell division will give rise to daughter cells with even more accumulated damage. Eventually, all checkpoints become nonfunctional, and rapidly reproducing cells crowd out normal cells, resulting in a tumor or leukemia (blood cancer).