Cancer is one of the deadliest diseases known in human beings. A report of 1993 suggested that 530,000 people died of cancer in the United States . In India, more than 1 million people suffer from cancer and large number of deaths are reported from the same annually . With the discovery of this deadly disease, world became inquisitive to know the causes of cancer. In 1950, an international symposium was organized by the World Health Organization and variation in different types of cancer found in different areas of the world were discussed whose result intrigued the people . It came out that people who migrated from their homeland to other areas of the world ought to develop the cancer which was endemic to the new area where they have settled. This inferred that most of the cancers have environment origin rather than genetic . This symposium led to the formation of International Agency for Research on Cancer (IARC) in 1965 whose main objective was set to conduct multidisciplinary investigation to find out the causes of cancer in humans . Although certain synthetic agents are also known to cause cancer in humans along with some oncogenic genes. The mutations in certain genes lead to formation of tumours . Thus, the main causes of cancer can be classified into three categories- physical, chemical and genetic.
Causes of Cancer in Humans
Cancer is a condition in which the normal cells of any body part lose the property of contact inhibition, i.e., the property of cells to stop multiplying and proliferating after coming in contact with other cells. As a result of this, the normal cells turn into cancerous or oncogenic cells which keep on multiplying, forming a cyst or tumour. Although, it’s not always necessary that a cyst be seen. The example is of the leukemia or blood cancer. Further, cancer is of two types; one which remain confined to their original location and continues to grow therein, termed as Benign Cancer and the other which shows the property of metastasis in which the tumour breaks and invade other cells through blood, termed as Malignant Cancer, which is generally fatal . The early diagnose of the cause of this disease was based on epidemiological studies and the cancer-causing agents, carcinogens were generally associated with certain occupations. In 1713, a study came out that most of the nuns in hospitals suffer from breast cancer. This was linked to their celibate life . Similarly, in 1775, a thesis came out that the chimney sweeps in factories generally suffer from the cancer of scrotum due to exposure to the soot particles . In 1895, a scientist named, Wilhelm Conrad Rontgen discovered X-rays which was a great breakthrough in the fields of science but a decade after this discovery, the cases of skin cancer amongst radiologists rose across the world . Though, some non-occupational causes were also coming out during this era. With time and development in technology, the studies shifted from theoretical to practical basis. The physical carcinogens were identified as certain non-ionizing radiation such as UV rays and certain ionizing radiation like X-rays and Gamma rays . Medical radioisotopes also became one of the major causes of this disease. In the late 1960s, radioactive phosphorus (34PO4) was commonly used for the treatment of Polycythemia which resulted in leukemia in high number of patients. Also, in the beginning of late 1960s, pharmaceuticals and chemicals came to be known as a leading cause of cancer. High rates of renal-pelvis carcinoma and lymphomas were observed in users of high doses of phenacetin and the patients who were on certain immunosuppressants given during organ transplants respectively . Further, tobacco smoke was found to greatly attribute to the lung cancer.
With the discovery of the Mouse leukemia and chicken leukemia viruses, scientists became eager to find out the viral carcinogens in the case of human cancer. Several viruses are accountable for causing 15% of the cancers in humans . The viruses accounted for inducing tumours in human are retro-viruses, non-retroviral RNA viruses and DNA viruses. In fact, it is believed that prevention from these viruses is the second-best option to prevent cancer after quitting tobacco. Some animal retroviruses, commonly called as acute transforming retroviruses, transduce oncogenes (v-onc) which derive from cellular proto-oncogenes (c-onc) and have the ability of inducing cell transformation in vitro as well as in vivo . On the other hand, in other retroviruses such as the complex human T-cell leukemia, virus type-I (HTLV-I), the transforming capacity is linked to the activity of authentic viral genes . As any change in the body is controlled by the activity of genes and the proteins they produce, hence these oncogenic viruses have genes called viral oncogenes that induces mutations, leading to faulty protein production. Further, certain normal cells of the body contain a set of genes called, cellular oncogenes or proto-oncogenes which could lead to oncogenic transformation of cells if activated under certain conditions . Therefore, the people, especially children, having this disease in their family pedigree should be more cautious and ought to take prevention against all type of carcinogens.
It should also be noted that in smoking and alcohol use accounts for more than one in every three of the 7 million deaths worldwide and still these products are highly consumed across the globe.
Conclusion
Cancer being one of the deadliest diseases in human beings accounts for a large number of deaths across the globe. It is a condition in which normal cells of the body loses the property of contact inhibition and turns into cancerous cells. The agents responsible for causing cancer are known as carcinogens and can be physical, chemical and biological. In 1965, International Agency for Research of Cancer was formed whose main objective was to determine the causes of cancer in humans and hence several studies were proposed for the same. In early 18th century, causes of cancer were linked to the environment and occupation of the patients. At this time, certain chemical carcinogens were also discovered. With further advent of technology, study was shifted to an epistemological phase. The radiations like UV, X-rays and Gamma rays and certain radioactive isotopes used for medical treatment in early times were accounted as the physical carcinogens. On the other hand, certain chemicals like tobacco and some immunosuppressants given to patients came out as chemical carcinogens. In addition to this, scientists broadened their research to the biological carcinogens and found certain viral oncogenes like retroviruses as a major cause of cancer in humans. These carcinogens alter the genes, causing mutations which lead to faulty protein production, responsible for this disease. Some cells of the body even contain set of oncogenes or proto-genes which when activated under some conditions induced tumours. Hence, one must take prevention from these carcinogens and adopt a healthy lifestyle to stay away from this disease.
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By Atavika Chandan
chandanatavika@gmail.com
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