Normal cells do not live forever. Under certain circumstance, cells are programmed to die, particularly during embryonic development. Cells that become damaged beyond repair normally commit suicide for the ‘greater good’ of the organism.
However, cancer cells have forgotten how to die and they divide at all cost. The genes that control cell division are damaged or break down. The resulting cells become immortal and no longer carry out their functional role-such as that of a skin, lung cell or eye cell. Two types of gene are normally involved in controlling the cell cycle-oncogenes, which start the cell division process, and tumor-suppressor genes, which switch off cell division.
In their normal form, both kinds of genes work as a team, enabling the body to perform vital tasks such as repairing defective cells and replacing dead ones. But mutations in these genes which either inherited or induced can disrupt these finely tuned checks and balances resulting to abnormal growth of cells termed as cancer.
Causes of Cancer
The following factors implicated in triggering cancerous changes in susceptible individuals have been identified :
Ionizing radiation ; Sources of high energy ionizing radiation such as ultraviolet light from the sun, gamma radiation from nuclear power and atomic bombs, X-ray radiation from medical treatment.
Inherited defective genes [familial factors] ; Some forms of cancer are thought to be triggered by defective genes that are inherited. There is a genetic vulnerability among some people to developing cancer.
Viruses ; A number of cancers are thought to be triggered by viral infections, for instance lymphomas. The virus splices its own DNA into the human chromosome, causing human genes to be upset.
Alcohol and dietary factors ; A diet high in total fat, especially one that includes large quantities of fatty, burned and/or preserved meats, has been implicated in the development of bowel cancers. High fats diets slow the passage of food through the gut giving time for cancer causing irritants to form in the bowel. High alcohol intake increases the risk of mouth, throat, liver and pancreatic cancers.
Environmental poisons ; Chronic exposure to carcinogens greatly accelerate the rate at which dividing cells make errors. Synthetic and natural examples include benzene, asbestos and the tar of tobacco smoke.