Discuss "cancer" in terms of cell cycle regulation and the health of both humans and animals.
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Cancer is a disease that can occur when the cell cycle is improperly regulated and a cell is allowed to divide when division should otherwise be aborted. There are various checkpoints in the cell cycle that monitor whether the previous step in the cell cycle was completed correctly. For example, a normal cell will be prohibited from entering the S phase of the cell cycle if its DNA is damaged. However, if a mutation renders a checkpoint protein dysfunctional, then the cell cycle will proceed through that checkpoint without proper surveillance. This will result in mutated daughter cells that will be able to divide once again unchecked. Accumulation of these daughter cells could occur almost anywhere in the body reeking havoc on the tissue structure and likely affecting the normal function of that tissue or organ. This tumor may not right away affect the health of the organism it inhabits, however. If division continues to occur the tumor may metastasize and invade adjacent tissues, including the blood and lymph. This metastasis of tumor cells can be deadly for the organism as these cells can settle in various other organs in the body and affect their proper function.