Origins of cancer
Cell division or cell proliferation is a physiological process that occurs in almost all tissues and under many circumstances.
Normally the balance between proliferation and programmed cell death is tightly regulated to ensure the integrity of organs and tissues . Mutations in DNA that lead to cancer disrupt these orderly processes. The uncontrolled and often rapid proliferation of cells can lead to either a benign tumor or a malignant tumor (cancer). Benign tumors do not spread to other parts of the body or invade other tissues, and they are rarely a threat to life unless they extrinsically compress vital structures. Malignant tumors can invade other organs, spread to distant locations ( metastasize ) and become life-threatening.
Molecular biology
Cancers are caused by a series of mutations. Each mutation alters the behavior of the cell somewhat.
Carcinogenesis , which means the initiation or generation of cancer, is the process of derangement of the rate of cell division due to damage to DNA . Cancer is, ultimately, a disease of genes . In order for cells to start dividing uncontrollably, genes which regulate cell growth must be damaged. Proto-oncogenes are genes which promote cell growth and mitosis , a process of cell division, and tumor suppressor genes discourage cell growth, or temporarily halt cell division in order to carry out DNA repair . Typically, a series of several mutations to these genes are required before a normal cell transforms into a cancer cell.
Proto-oncogenes promote cell growth through a variety of ways. Many can produce hormones , a "chemical messenger" between cells which encourage mitosis, the effect of which depends on the signal transduction of the receiving tissue or cells. Some are responsible for the signal transduction system and signal receptors in cells and tissues themselves, thus controlling the sensitivity to such hormones. They often produce mitogens , or are involved in transcription of DNA in protein synthesis , which creates the proteins and enzymes responsible for producing the products and biochemicals cells use and interact with. |
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Mutations in proto-oncogenes can modify their expression and function, increasing the amount or activity of the product protein. When this happens, they become oncogenes , and thus cells have a higher chance to divide excessively and uncontrollably. The chance of cancer cannot be reduced by removing proto-oncogenes from the genome as they are critical for growth, repair and homeostasis of the body. It is only when they become mutated that the signals for growth become excessive.
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