With only a defective APC product available, chromosomes are lost from the spindle producing aneuploid progeny. The cells in the later stages of the disease show additional types of damage such as deletions of p53 and another tumor-suppressor gene. Note that each of the mutations shown probably occurs in one cell of the type affected. This cell then develops into the next stage of the progression. The mutations do not necessarily occur in the order shown, although they often do.
Cancers become more common as one gets older.
The graph shows the death rate from cancer in the United States as a function of age. The graph also explains why cancer has become such a common cause of death during the twentieth century. It probably has very little to do with exposure to the chemicals of modern living and everything to do with the increased longevity that has been such a remarkable feature of this century. Chemicals that cause cancer are called carcinogens . This is because a cell is most susceptible to mutations when it is replicating its DNA during the S phase of the cell cycle .