Cancer is a group of diseases which are considered fatal by most of them. So, the policy of “Prevention is better than cure” exactly holds good for Cancer. Hence the knowledge of the causes of Cancer is very important for every individual in prevention of cancer. Most of the causes of cancer are environmental and a few are genetic related. Environmental factors are mostly modifiable and if extra care is taken to prevent them, the risk of getting cancer can be reduced to a greater extent.
Cancer is due to effect of mutagens, the agents which cause mutation of DNA which is responsible for uncontrolled cell growth. These mutagens are termed as Carcinogens. Not all carcinogens are mutagens. The causative factors of cancer can be broadly divided into:
1. Environmental factors : Chemicals, Radiation.
2. Individual factors : Diet, exercise, Substance abuse like alcohol, tobacco etc;
3. Genetic factors
Chemicals : Among the chemical carcinogens, the first to be discussed about is tobacco. Tobacco smoking is the leading cause of lung cancer, one of the most common cancers in the world. Tobacco has various known 40 to 50 chemical carcinogens responsible for lung cancer. Apart from tobacco, few chemicals are responsible for occupational cancers like Asbestos causing mesothelioma, Benzene causing leukemia. Some agents like silica and cobalt also cause cancer.
Radiation : In the recent practice of medicine, there is much scope of patients getting exposed to frequent radiation as most of the Clinicians order for radiological investigations in order to support their clinical diagnosis. The radiation exposure due to medical imaging cause cancers due to ionising radiation. Young people are more prone to radiation induced cancers than elders. The risk increases many times to the baby in utero when the pregnant woman is exposed to radiation. So, Pregnancy is an absolute contraindication to radiation exposure. Non ionising radiation in the form of ultraviolet radiation also causes some skin cancers when exposed chronically.
Diet: Diet plays a major role in cancer etiology. Diets rich in fat, high salt content, tanned foods, eating more of junk foods with less fruits and vegetables are predisposing factors for cancers. These diet variations are risk factors for development of gastric and colon cancers.
Physical activity and Exercise: Regular physical activity and exercise reduces the risk of cancers by reducing overweight and maintaining hormonal balance. In western countries about 30% of cancer deaths are due to Obesity.
Substance abuse: Alcohol is the most common cause of substance abuse and its chronic consumption leads to liver and pancreatic cancers.
Genetic factors : Most of the cancers are not hereditary. The hereditary cancers are those which carry the defective genes from generations. The presence of genetic defect particular to some specific cancers increases the risk to 70 times more of having that cancer in the lifetime of that individual. For example presence of BRCA1 and BRCA2 in the individual increases the risk of having breast and ovarian cancers.
Infections: Specific infections of bacteria,virus and parasites predispose to few cancers. Examples are:
Virus: Hepatitis B and C – Liver cancer
Epstein Barr virus – B cell cancers
Human papilloma virus – Cervical cancer.
Bacteria: H.pylori bacteria causes gastric cancer.
Parasites: Schistosoma – Bladder cancer.
Though there are many listed causes of cancer, the development of cancer and cause relationship varies from person to person and place to place.