Carcinogenesis is the process of formation of cancer cells as a result of cancer-causing triggers such as viruses and bacteria, physical agents, chemical agents, genetic or familial factors, dietary factors, and hormonal agents.  The causative factors are called carcinogens.  3 steps in cellular carcinogenesis are initiation, promotion, and progression.


Table Of Contents

1. Introduction

2. Phases of carcinogenesis 

3. Common carcinogenic agents

      3.1 Viruses and Bacterium

     3.2 Physical Agents

     3.3 Chemical Agents

     3.4 Genetic and Familial Factors

     3.5 Dietary Factors

     3.6 Hormonal Agents

     3.7 Immune System Failure


Phases of carcinogenesis 

  1. During the initiation, carcinogens; chemicals, physical factors, and biologic agents cause genetic alteration against the normal cells. As a result, DNA is seriously damaged which in turn result in mutation. Mutation can significantly affect the normal physiology of our body.

  2. During the promotion, there is a repeated exposure of mutant cells which further complicate the issue. Prolonged exposure of mutant genes to the carcinogens results in the faulty expression of genetic information. Furthermore, the altered DNA may result in abnormal growth and development of normal cells through uncontrolled multiplication resulting in a cancerous mass.

  3. Progression is the third stage in which the damaged cells will further continue the process of malignant behaviour resulting in the exchange of normal cell`s DNA with that of abnormal cells.


Common carcinogenic agents

  1. Viruses and Bacterium

Viruses can cause an irreversible aberration and derangement of the genetic composition of cells. Some of the most common carcinogenic viruses are, Epstein-Barr, Herpes simplex virus type II, cytomegalovirus, and human papillomavirus types 16, 18, 31, and 33. Some of the bacteria such as Helicobacter pylori has proved to be the cause of gastric cancer.

  1. Physical Agents

Chronic exposure to sunlight, radiation, irritants, and some of the inflammatory agents such as tobacco can result in carcinogenesis. In some cases, poor clothing styles (sleeveless shirts or shorts) and past history of internal injuries can result in carcinogenesis.

  1. Chemical Agents

Tobacco smoking is the most common well-known carcinogen. Chronic smoking result in cancers of the lung, head and neck, oesophagus, pancreas, cervix, and the urinary bladder. The prolonged usage of chemical substances such as alcohol, amines, aniline dyes, formaldehyde, arsenic, plastic, polyvinyl compounds, lead and some radioactive agents increase the risk of cancer.

  1. Genetic and Familial Factors

Genetic factors can contribute to about 40% of new cancer cases and it is increasing from time to time. Genetic influence is very strong in case if both the parents had a carcinogenic tendency. In addition to the genetic factors, familial practices- cultural practices,  lifestyle factors and high-risk family behaviours can increase the risk of carcinogenesis.

  1. Dietary Factors

About 35% of all cancers are due to high-risk dietary intake. Dietary substances including excessive use of fats, alcohol, highly salted and smoked meats, partly cooked meats, a diet low in fibre can induce carcinogenesis. However, dietary substances that appear to reduce cancer risk are high-fibre foods, vegetables like cabbage, broccoli, cauliflower, Brussels sprouts, kohlrabi, carotenoids can prevent the growth of cancer cells in their long-term usage. Obesity can also further increase the risk of inducing cancer process.

  1. Hormonal Agents

Androgens; estrogen and progesterone take the lead role to trigger the carcinogenesis. Breast cancer, prostate, and uterus cancers are closely linked with the hormonal imbalance in women. Breast cancer is the most common cancers in females caused by birth control agents - oral contraceptives, prolonged estrogen replacement therapy may result in endometrial and ovarian cancers.

  1. Immune System Failure

The immune system plays an important role in the incidence of cancer. Most of the cancer cells can attack the body cells that are immunocompromised. Our immune system is driven by T-lymphocytes, B-Lymphocytes, WBCs and some of the glandular secretions. Abnormal cell pattern in these will further deteriorate the functions of the immune system resulting in chronic infections, bleeding, swelling and anaemia. A healthy immune system is able to fight against the cancer cells in a number of ways. When a cancer cell enters into the system, immune recognizes this as a foreign body (antigen) which in turn initiate the defence mechanism to counter the carcinogenic factors. But the antigens produced by carcinogens are known as tumour-associated antigens or tumour cell antigens capable of stimulating both cellular and humoral immune responses. If the lymphocytes and macrophages are active, the chances of domination from cancer cells is less likely.





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