What Is Cancer?
Cancer is fundamentally a disease of failure of regulation of tissue growth with the potential to invade or spread to other parts of the body, which involves abnormal cell growth and gene variation. Possible signs and symptoms of cancer include a lump, abnormal bleeding, unexplained weight loss, prolonged cough, and a change in bowel movement. Many cancers can be prevented by keeping healthy lifestyle, which includes not smoking, not drinking too much alcohol, eating more vegetables, fruits and whole grains, not eating too much processed and red meat, maintaining a healthy weight, avoiding too much sunlight exposure, and vaccination against certain infectious diseases.
Classification of Cancer
Tumors can be either benign or malignant. Benign tumors are not cancerous, tumors cells do not extend to other parts of the body. Malignant tumors are cancerous, tumor cells invade nearby tissues and extend to other parts of the body, which is termed as metastasis. There are hundreds of different cancers from histological point of view which are grouped into six major categories:
Factors Affecting Cancer Development
There are a number of intrinsic and extrinsic features coupled with the progression of cancer. The intrinsic features consist of age and hormonal significance of the individual, ancestral history, and hereditary make. The external features comprise diet and lifestyle, smoking and alcohol use, contact to deadly chemicals and radiation, several infections, etc.
Stages of Cancer
In vitro, in vivo, and epidemiologic studies have enabled researchers to affirm that neoplastic pathogenesis is a complex process from functional aspects which can be divided into three distinct stages involving changes in the genome’s structure.
|Initiation||It forms the first stage of carcinogenesis characterized by irreversible genetic changes which predispose vulnerable normal cells to malign evolution, and immortality has been concluded from various studies. It is a speedy, permanent phenomenon which is transmitted to daughter cells. After successive genotypical and phenotypical changes are initiated, the cell is converted into a neoplastic one. The initiated cell is similar to the remaining cells from a phenotypical perspective and undergoes mutations which induce proliferation but not differentiation. It has been well validated that DNA damage is the prime event to initiate chemical carcinogenesis which can be repaired by enzymatic mechanisms. Proliferating cells are unable to fix the damaged DNA because of less time and remove covalent bonds that chemicals make with the DNA known as adducts.|
|Promotion||Metabolic activation is necessary for promoters to cause its effect and does not interact directly with DNA. They contribute to fasten mutations, enhance cell proliferation in susceptible tissues, augment alterations in genetic expression, and change cellular growth control. They can also indirectly damage DNA via oxidation. Promoters impede the natural inhibition of the quiescent cells or in G0 by gap junctions. Its most important activity is mitogenesis, wherein genotoxicity and mutations are not obligatory at this stage. In order to be efficient, the exposure with promoter must be for weeks, months, and years, and its efficacy depends on its concentration in the target tissue. If promoter is removed or somehow made unavailable, a regression in cell proliferation occurs via induction of apoptosis. Hence, promotion is a reversible stage at early stages and can be modified by physiological factors limiting the extent of experimental carcinogenesis.|
|Progression||Histopathology identifies the sequence of lesions between initiation and promotion which is called as preneoplastic lesions or benign neoplasias. The last stage of carcinogenesis is the most extended wherein transformation into malign lesions occurs undergoing labeled progression. Genetic and epigenetic mechanisms lead to the formation of a neoplastic phenotype, and cell proliferation is independent of stimulus in progression. Alterations in the biochemical, morphological, and metabolic characteristics of cells occur in progression. Moreover, progression is characterized by faster growth, irreversibility, genetic instability, invasion, and metastasis. Angiogenesis that occurs by epigenetic mechanisms is indispensable to neoplastic progression, and acquisition of such phenotype heads the development of features that contribute to malignancy, whereas its inhibition delays neoplastic development.|
1. Rashid S. Cancer and Chemoprevention: An Overview. Springer Singapore, 2017.