Cancer is a genetic disease because it can be traced to alteration within specific genes, but in most cases, it is not an inherited disease. The genetic alterations that lead to most cancers arise in the deoxyribonucleic acid (DNA) of a somatic cell during the lifetime of affected individual. Because of these genetic changes, cancer cells proliferate uncontrollably, producing malignant tumour that invade surrounding healthy tissue. As long as the growth of tumour remains localized, the disease can usually be treated and cured by surgical removal of tumour. But malignant tumours tend to metastases, that is, to spawn cells that break away from the parent mass, enter the lymphatic or vascular circulation, and spread to distant sites in the body where they establish lethal secondary tumours (metastases) that are no longer amenable to surgical removal. Despite, various exogenous and endogenous factors are known to affect the normal pattern of cell growth, by which cell becomes a cancerous. Species specificity and identity of biological organisms maintain by the unchanged genomic structure throughout their life period. The ratio of cell growth and cell death is strictly balanced through developmental and homeostatic processes in multi-cellular organisms (Bolsover et al, 1997).
1.1 Historical Backgrounds
Rig Veda, an ancient Indian scripture compiled five thousand years ago, and records the science of healing. A Fatal tumor in the throat is described in Atharva Veda (Mehta and Bansal, 2004). The Egyptians (c.1600BC) were the first to realize that tumors arising in various parts of the body differ in their behaviors and therefore, should be treated in different ways. References were also made to the treatment of such tumors by excision and with arsenical compounds (Mehta and Bansal, 2004). The origin of word “cancer” is credited to Greek physician Hippocrates, (Greece, c.460-370BC) divided tumor into two broad groups, according to their behavior: a) the “innocuous” and b) the “dangerous”. He also coined the terms “Karkinos” for non-healing ulcerating tumors and “Karkinoma” for solid tumors. Both terms are derived from Greek term “Karkinos” meaning crab (Mehta and Bansal, 2004). It was Aurelius Celsus (c 30 AD), who gave a much clearer description of cancer, separating inflammatory swelling from neoplasm. Galen (AD 131-201) considered a tumour to be an entity that existed contrary to the law of nature, representing a true “new growth”. Galen was also apparently aware of the phenomenon of metastasis. The term “cancer” appeared in literature much later, derived from the Latin term “cancrum”, also meaning a “crab”. Recamier coined the term “metastasis” in 1829, when he demonstrated secondary tumors in the brain of patient with breast cancer. However, the thoughts that metastasis spread by a liquid dominated during this period (Mehta and Bansal, 2004). Development of microscope in the 17th century, helped in establishing the specificity of histology, which culminated in the introduction of a revolutionary new concept by Virchow (1821-1902) that new cells were continuously being formed the basis of classification of tumors today (Mehta and Bansal, 2004).
1.2 Definition
No satisfactory complete definition of neoplasia exists. The definition of Wills (1952), however remain one of the most widely cited and useful. “A neoplasia is an abnormal mass of tissue, the growth of which exceeds and is uncoordinated with that of the normal tissue and persists in the same excessive manner after cessation of the stimuli which evoked the change”.
1.3 Etiology of cancer
The major insights into etiology of cancer can be obtained by epidemiological studies that relate to particular environmental (agents acting on the body from outside), and genetic (acting within the body) factors. Some of the causative factors are as follow:
Chemical substances
Chemical substances of certain types have a propensity for causing mutations. For instance, various