Tian Xian

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WHAT ARE CARCINOGENIC SUBSTANCES?

External, environmental factors that constitute 80-90% of all causes of cancer include carcinogenic substances, exposure to radiation, and viruses. Internal factors include weakening of the immune system, heredity, old age, and lifestyle changes. According to a report from the WHO, 35% of carcinogenic substances are derived from food and beverages, and 30% come from smoking.

When speaking of carcinogenic substances, people usually think of food additives, agricultural chemicals, and so on. What exactly are carcinogenic substances? Carcinogens are substances that give rise to cell changes that eventually lead to tumor growth and cancer. Let me now explain how carcinogenic substances give rise to cancerous cells and tumors. The process of cancer formation takes place at two levels. The first level is called the initiation stage, while the second level is the promotion stage.

Table 14. Types of cancer metastasis

Lymphogenous metastasis	This is the type in which the cancerous cells of the disease float away from the cancerous tissue into the blood circulaltion and migrate to other parts of the body.
Metastasis in lymthic circulation	This is the type in which the cancerous cells of the disease flow to the outlying lymphatic knobs, circulating with the lymphatic fluid and invading the lymphatic glands one by one and eventually enter into the veins throught he left clavicle, and dispersing into the whole body.
Destructive metastasis	This is the type whereby the cancerous cells grow larger steadily and metastasize to adjoining organs, tissues, eg. invasion of cracinoma of stomach into the abdominal cavity to cause the type of carcinomatous peritonitis.
Contact metastasis	This is the type whereby cancerous cells metastasize metastasize to adjoining organs, eg. complication of carcinoma of stomach to neighbouring liver cancer.

Initiation is the process in which a particular carcinogen creates a drastic change in the cell’s DNA. The most familiar examples of such carcinogens are:

• trypase P1, P2 (chemical substances resulting from the burning of cigarettes, meat and fish)

• AF2 (food additive)

• mycotoxin yellow grain toxin B1mycotic toxin

• cyclic hydrocarbon (from vehicle emissions and cigarette tar)

• nitrosamine (nitrous acid and amine in food composed in the stomach)

• ultra-violet (UV) rays

• radiation

• hepatitis C virus (HCV)

• adult T-cell leukovirus (ATLV) etc.

Promotion is a second, less immediate process in which chemical substances are absorbed into the body that increase the probability of carcinogenesis. They accomplish this by forming cancer-promoting substances. Such substances alone do not have the power to cause cancer.

Examples of cancer-promoting substances are:

• cigarette smoke

• hormones

• bile acids (liquids composed of cholesterol formed in the liver)

• saccharin (an artificial sweetener)

• Phenobarbital (an analgesic and nervous system drug)

• alkaloid (substance contained in seaweed and other plants)

• whole globular ester (contained in croton oil)

Initiation and promotion differ in their manner of stimulating the growth of cancer. So long as normal cells do not react to carcinogens in either of these ways, they will not become cancer cells.

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