Causes of cancer

About Cancer is a chronic disease. As with any other chronic diseases, cancer has a multifactorial etiology (cause). Carcinogens are the substances which can cause cancer to humans.

1. Environmental factors: Environmental factors are responsible for at least 90 per cent of all human cancers. The major environmental factors identified include the following:

a. Tobacco: Tobacco in various forms of usage (e.g. smoking, chewing, sniffing) is the major environmental cause of cancers of lungs, larynx, mouth, pharynx, esophagus, bladder, pancreas and also kidney. It has been estimated that cigarette smoking is responsible for more than one million premature deaths every year throughout the world in the form of cancer, respiratory problems and also in many other way. There is hardly any organ system which is not affected adversely due to cigarette smoking.

b. Alcohol: Excessive intake of alcoholic beverages is associated with esophageal and liver cancer. Some recent studies have suggested that beer consumption may be associated with rectal cancer. It is estimated that alcohol contribute to about 3 per cent of all cancer deaths in the world.

c. Diet: Dietary factors are also related to cancer. Smoked fish and meat is related to stomach cancer (consumption of smoked fish causes cancer), less intake of dietary fiber can cause intestinal cancer, excessive beef consumption can lead to bowel cancer and a high fat diet can lead to breast cancer. A variety of other dietary factors such as food additives and contaminants are also blamed to be carcinogenic. Diet rich in vitamins, minerals and antioxidants reduce the incidence of cancer.

d. Occupational exposures: These include exposure to benzene, cadmium, chromium, arsenic, asbestos, polycyclic hydrocarbons, vinyl chloride, etc. Many others remain to identified. The risk of occupational exposure is considerably increased if the individuals also smoke cigarettes. Occupational exposures are reported to account for 15 per cent of all human cancers. Occupation like road construction and handling of coal tar causes cancer of skin. Chimney sweepers are prone to develop prostate cancer.

e. Viruses : An intensive search for a viral origin of human cancers revealed that hepatitis B virus can cause hepatocellular carcinoma (liver cancer). The Epstein-Barr virus (EBV) is associated with 2 human malignancies, Burkitt’s lymphoma and nasopharyngeal carcinoma. Cytomegalovirus (CMV) is a suspected oncogenic agent of classical Kaposi’s sarcoma. Human papilloma virus (HPV) is the main suspect of cancer cervix. Main causative agent of cervical cancer is most likely a virus, due to the fact that it is almost non existence among Christian nuns who are not engaged in sexual intercourse. Whereas the incidence is very high among females with multiple sex partners. Hodgkin’s disease is also believed to be of viral origin. The human T-cell leukemia virus is associated with adult T-cell leukemia/lymphoma in United States and southern part of Japan .

f. Parasites: Parasitic infections can also increase the risk of cancer. Schistosmiasis in Middle East causes carcinoma of the urinary bladder.

g. Others: There are numerous other environmental factors such as sunlight, aeration, air and water pollution, medications (e.g. estrogen) and pesticides which are suspected to be related to cause cancer. Exposure to sun can cause skin cancer in white people, that is why skin cancer is most commonly seen in Australia and New Zealand.

h. Customs, habit and life styles: Customs, habits and lifestyles of people may be associated with an increased risk for certain cancers. The familiar examples are the demonstrated association between smoking and lung cancer, tobacco and betel chewing and oral cancer etc. Kangri cancer is seen in Kashmir. This is due to holding an earthen pot full of burning coal, in front of abdomen during winter months to keep the body warm. The skin around umbilicus is exposed to constant heat, which causes skin cancer.

2. Genetic factors: Genetic influences have long been suspected . For example, retinoblastoma occurs in children of the same parent. Certain people are more likely to develop cancer (leukaemia) than normal children. However, genetic factors are less conspicuous and more difficult to identify. There is probably a complex interrelationship between hereditary susceptibility and environmental carcinogenic stimuli in the causation of a number of cancers.



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