Cancer



Cancer

In the normal circumstances, the proliferation of body cells is under strict control. The cells differentiate, divide and die in a sequential manner in a healthy organism. Cancer is characterized by loss of control of cellular growth and development leading to excessive proliferation and spread of cells. About 100 different types of human cancers have been recognized. Cancers arising from the epithelial cells are referred to as carcinomas while that from connective tissues are known as sarcomas. Methods for the early detection and treatment of cancers have been developed .However, little is known about the biochemical basis of cancer.
Incidence: Cancer is the second largest killer disease (the first being coronary heart disease) in the developed countries. It is estimated that cancer accounts for more than 20% of the deaths in United States. Based on the current rate of incidence ,it is believed that one in every 3 persons will develop cancer at sometime during his/her life. In general, cancers are multifactorial in origin .The causative agents include physical, chemical, genetic and environmental factors .A survey in USA has shown that about 90% of all cancer deaths are due to avoidable factors such as tobacco, pollution, occupation, alcohol and diet. Most of the cancers are caused by chemical carcinogens, radiation energy and viruses. These agents may damage DNA or interfere with its replication or repair.
Chemical carcinogens: It is estimated that almost 80% of the human cancers are caused by chemical carcinogens in nature .The chemicals may organic or inorganic in nature. In general, a chemically non-reactive pro carcinogen is converted to an ultimate carcinogen by a series of reactions .
Radiation energy: Ultraviolet rays, X-rays have proved to be mutagenic in nature causing cancers. These rays damage DNA which is the basic mechanism to explain the carcinogenicity of radiation energy. For instance, exposure to UV rays results in the formation of pyrimidine dimmers in DNA while X rays cause the production of free radicals. These types of molecular damages are responsible for carcinogenic effects of radiations.
Carcinogenic viruses: The presence of viral particles and the enzyme reverse transcriptase, besides the occurrence of base sequence in the DNA of the malignant cells, complimentary to tumor viruses indicate the involvement of viruses in the cancer. The viruses involved in the development of cancer, commonly known as oncogenic viruses.
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