According to the Proceedings of the National Academy of Sciences of the United States, cancer occurs when too many cells are allowed to grow. In cancerous cells, the normal control mechanisms of the cell are repressed, preventing the cell from stopping this abnormal growth and proliferation.
Normally, a healthy cell responds to signals from both within itself and from the rest of the body. Among other things, these signals can cause the cell to stop replicating or even undergo apoptosis. Apoptosis, which is also called programmed cell death, is one of the ways that the body can prevent cancer from developing. However, as explained by Nature.com, cancer is the result of mutations accumulating in the DNA of a cell. These mutations often prevent the cell from responding to the internal and external signals that tell healthy cells to stop growing or die. Because they do not respond to these signals, the cells begin to multiply and form a tumor.
While the tumor is growing, additional mutations occur in the cell’s DNA, according to Science.com. Some of these mutations are beneficial to the cancerous cells, so the tumors grow even larger. As these mutations are passed down to daughter cells, the entire mass becomes larger and larger. Eventually, some pieces may break away, or metastasize, and cause tumors to form in other parts of the body.