Causes of Cancer
Scientists have identified the cellular genes that code for those proteins which jointly control and regulate cell growth and division. These genes are of two broad categories proto oncogenes and tumor supprerssor genes. Any change i.e. mutations in these genesparticularly in the proto oncogenes, shatters the cellular controls over growth and division rendering the concerned cells carcinogenic. A mutated proto oncogene is called oncogene.
Mutations in proto oncogenes and other related genes may occur spontaneously due to a variety of factors originating in the cells themselves. These may also occur due to physiological disorders in the body beside this, certain external environmental factors have alsobeen indentified as carcinogenic mutagens. It has been found that incidence of cancer increases in a population exposed to ionizing radiations (X-rays, gamma rays and ultlraviolet rays ) and certain chemicals such as those present in chimney smoke. Chemical present in cigarette smoke such as vinyle chloride, benzopyrenes and nitro so nor nicotine, are known to cause lung cancer.