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Causes of cancer
Last reviewed: 23.04.2024
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Nutrition as a cause of cancer
Excess in the diet of any of the main ingredients of food - proteins, fats and carbohydrates - promotes the development of cancer, since this excess in one way or another creates metabolic disorders. For example, increased cholesterol in the diet increases the incidence of lung cancer. There is a high correlation between the risk of breast cancer and calorie diet, the consumption of easily digestible carbohydrates. An increase in excess in the diet of animal proteins also increases the incidence of cancer, which is largely due to the influence of animal fat and cholesterol.
The consumption of salted meat, especially when combined with smoking, is considered the main risk factor for cancer of the larynx. The relationship between the amount of sugar in the diet and the frequency of breast cancer is revealed. An inverse correlation was established between the consumption of starch and the incidence of colon cancer. Starch is a good substratum for the production of butyrate, which has a protective effect on the epithelium of the large intestine. Micronutrients contained in canned foods (salt, nitrites) and phosphates damage the mucous membrane in the digestive tract, which increases the possibility of mutagenic exposure.
Protective factors include calcium, which reduces the permeability of the mucous membrane, and antioxidants (vitamin C, carotenoids), trace elements (selenium) and plant anti-carcinogens (phytoestrogens, flavonoids, tea polyphenols).
Epidemiological studies show that excess fat in a diet (both plant and animal) contributes to the development of cancer. Factors of the pro-carcinogenic effect of fat are as follows:
- influence on the metabolism of carcinogens (including the intestinal microflora, which is supposed to increase the conversion of bile acids into carcinogenic metabolites);
- direct action on the tissues in which the tumor develops;
- action on the endocrine system;
- influence on immunity systems and hemocoagulation.
Excess body weight increases the risk of almost all forms of cancer, and the more it is, the higher the risk. The scientific literature has accumulated a lot of data confirming the connection of obesity with the development of cancer of the kidney, colon, lungs, mammary glands and the female sexual sphere.
At the expressed obesity the risk to die of a cancer is higher for men on 52%, and at women for 62% in comparison with people having normal weight of a body.
As a result of a study in the United States, the following data were obtained. Among women with maximal body weight, the cause of death of uterine cancer was 6 times more often, cancer of the kidney - 5 times, cervical cancer - 3 times, breast, gall bladder, pancreas and esophagus - 2 times more often compared with control groups.
Among men with a maximum body weight, liver cancer was 6 times more likely, pancreatic cancer 2 times, gallbladder, stomach and rectum 75% more likely than control groups.
In recent years, considerable attention has been paid to the possible protective role of so-called plant fibers, which include cellulose, pectin, and the like. It is believed that food containing plant fibers (in particular, cabbage, peas, beans, carrots, cucumbers, apples, plums, etc.), can help reduce the incidence of cancer of the gastrointestinal tract. It is still not determined whether the protective property of dietary fiber is related to their quantity or to the function of certain components. Dietary fibers affect the process of fermentation in the large intestine (resulting in the production of short chain fatty acids such as butyrate, an inhibitor of apoptosis) and increase the volume of fecal masses (thus leading to a decrease in the concentration of carcinogens in the colon lumen).
Some plant components, containing primarily lignins, as a result of metabolism in the intestine can increase the level of estrogens in the body. Such plants include soy.
The most favorable effect of a rational way of life is noted among non-smokers who do not drink alcohol and meat and eat fresh vegetables daily. In this group of persons, the annual mortality from tumors in standardized indicators was 324 cases per 100,000 people. Compared with 800 cases per 100 thousand people. In people with an opposite in nature way of life. At the same time, protein starvation contributes to a significant decrease in the activity of immunity and is also highly undesirable.
Causes of Cancer: Smoking
According to experts from the WHO Committee on Tobacco Control, there is now convincing evidence that there is a causal link between smoking and lung cancer. They are based on numerous retrospective studies conducted in a number of countries. These studies invariably reveal a close relationship between lung cancer and cigarette consumption. At the same time, the risk of developing lung cancer is directly related to the number of cigarettes smoked, the age at which smoking was started, the frequency and depth of the tightening, etc.
To illustrate the dependence of the incidence of lung cancer on the number of cigarettes smoked, the following data can be cited: in the United States, people who smoke twice a day on cigarette packs or more, the risk of lung cancer is 24 times higher than that of non-smokers.
Smoking and alcohol use are the leading risk factors for cancer of the head, neck and mouth, including cancer of the lips, tongue, gums, larynx and pharynx. Approximately 400 thousand new cases of these diseases are diagnosed globally every year, and most of them occur in developing countries. The researchers found that tobacco smoke destroys the molecules of antioxidants in saliva and turns it into a mixture of hazardous chemicals. Arsenic, nickel, cadmium and beryllium present in cigarette tobacco can (up to 10% for some of them) pass into tobacco smoke when smoking. Exposed to the influence of tobacco smoke, saliva not only loses its protective properties, but even becomes dangerous and contributes to the destruction of cells in the mouth.
Smoking also increases the incidence of cancer of the esophagus, gallbladder and pancreas. In published prospective studies conducted in the United States, a relationship was established between smoking and the risk of developing pancreatic cancer. Two- and three-fold increased risk of pancreatic cancer in smokers compared with non-smokers.
The mechanism of the effect of smoking on the incidence of cancer is not established. It is believed that specific carcinogens fall into the pancreas or hematogenous way, or with reflux of bile. Cessation of smoking can prevent 25% of deaths from pancreatic cancer.
There are a large number of publications that testify to the carcinogenic effects of alcohol in the development of cancer of the upper digestive tract, primary liver cancer, breast cancer, rectum,
Despite the impressive amount of scientific information confirming the carcinogenicity of alcohol consumption for humans, the mechanism of carcinogenic action of alcohol is still not clear. According to experimental studies, ethanol, as such, is not carcinogenic. It is believed that ethanol plays the role of a promoter of carcinogenesis.
[6], [7], [8], [9], [10], [11],
Reproductive history
This factor plays an important role in the etiology of tumors of female genital organs. This, especially the features of menstrual, sexual, childbearing and lactation functions. So, the early age of the onset of menstruation (menarche) and late menopause increase the risk of developing breast cancer, carcinoma of the uterus and ovary. In women who had a menarche age of 15 years or more, compared to women who began menstruating to age 13, the cancer risk of breast cancer is reduced by half. In women with late menopause (54 years or more), cancer risk was increased 4-fold compared with women who had menopause before 47 years of age. Childbirth reduces the risk of developing breast cancer. Compared with a woman who never gave birth to a woman who gave birth to one child, cancer risk is reduced by 50%. Moreover, with the increase in the number of pregnancies that have resulted in childbirth, the risk of developing breast cancer continues to decline, and a woman who has given birth to three or more children has a 65% lower risk than women who have not given birth. Early labor is also a factor that reduces the risk of developing breast cancer. Thus, in women who gave birth to the first child under 25, cancer risk is 35% lower than in women who had their first childbirth after 35 years.
Causes of cancer: ionizing radiation, insolation
Ionizing radiation, found in the human habitat, consists of a natural (natural) radiation background and ionizing sources, the origin of which is determined by human activity.
The radiation (ionizing) natural background is made up of three types of sources of ionizing radiation. The first of these is the cosmic rays reaching the surface of the Earth, the second is the radiation of radioactive elements that make up the earth's crust (soil, rocks, sea water, in some cases, soil water). The consequence of the presence of radioactive elements in rocks is their presence in building materials and ionizing radiation by stone buildings. Of the rocks, as well as of the building materials produced from them, radon gas is slowly released in one or another quantity. It is also isolated from the structural elements of stone buildings. These circumstances determine the presence of radon in the seawater and waters of some sources, as well as in industrial and residential areas. Finally, the third type is the ionizing radiation of radioactive nuclides that make up the body of people (and animals). Interestingly, each of these three types of sources of ionizing radiation currently contributes approximately the same contribution to the overall level of the natural radiation background.
The total radiation load per person in modern society, according to existing estimates, is determined approximately 2/3 by the action of the natural background of ionizing radiation and by 1/3 the influence of anthropogenic sources of it. Among the latter, the largest share is the use of ionizing radiation in medicine (diagnosis and therapy). Radiation load of this origin reaches approximately 30% of the total load per person of ionizing radiation from all possible sources. The radiation load from other sources of anthropogenic origin, including radioactive atmospheric precipitation, occupational radiation hazards and radioactive waste, is only a few percent (about 2%) of the total load originating from all sources.
According to experts on radiation hygiene, the cumulative carcinogenic effect of ionizing radiation accounts for only about 1-10% of all malignant tumors in humans.
Analysis of cases of leukemia in Greece, starting in 1980, showed that the incidence of diseases in children under 12 months of exposed pre-natal exposure due to radioactive fallout from the Chernobyl accident is 2.6 times higher than in unirradiated ones.
The effect of small doses of radiation on the thyroid gland of children is the cause of a sharp increase in the incidence of papillary thyroid cancer. In this case, the peak of their occurrence is observed in the 20 - 25-year period after the radiation exposure in doses of 10 - 60 Gy.
The second important radiation-causing carcinogen of the human environment is solar ultraviolet radiation. Based on epidemiological studies, it was concluded that the vast majority of different forms of skin cancer should be considered as a geographical pathology associated with prolonged excess exposure to solar ultraviolet rays. Important etiological significance of solar ultraviolet rays are also for cancer of the lip and malignant skin melanoma.
Activation of the protooncogene causes ultraviolet radiation with a wavelength of 160-320 nm, which is absorbed by DNA with the transition of its bases into an excited state. After this, DNA can rebuild its molecular structure and move to a new stable state. Simultaneously with the transformation of normal cells into cancerous ultraviolet quanta, the immune and reparation systems of the body are suppressed.
It is known that as a result of anthropogenic impacts on the stratosphere, it is possible to reduce the thickness of its ozone layer, which leads to an increase in the flux of ultraviolet rays reaching the human habitat. Meanwhile, an increase in the intensity of ultraviolet radiation of the sun by 1% increases the incidence of skin cancer by 2%.
[12], [13], [14], [15], [16], [17],
Pollution of the environment as a cause of cancer
The increase in the incidence of malignant neoplasms is now believed to be due to an increase in the level of contamination of the external environment by various chemical and physical agents possessing carcinogenic properties. It is considered that up to 85 - 90% of all cases of cancer are determined by the impact of environmental carcinogens. Of these, about 80% refers to chemical carcinogens, mainly polyaromatic hydrocarbons (PAHs) and nitrosamines (NA). As a result of systematic studies of the level of pollution of PAH's natural media, the global nature of its distribution was revealed. It has been established that the concentration of PAHs and primarily benzo (a) pyrene in the environment is correlated with the blastomogenic effect.
At present, the growing general contamination of soil and reservoirs with nitrites and nitrates is of great concern, in particular, due to the expansion of the use of nitrogen fertilizers. It causes the appearance of these agents in plants and plant foods, feed and even animal products, for example in milk.
An important aspect of this problem is that nitroso compounds can form in the body of animals and humans. There is ample evidence that endogenous synthesis of nitroso compounds can occur in humans and animals at concentrations of nitrites and nitrates that actually enter the body with food.
The problem of nitrate contamination still remains relevant for some European countries, but as a result of research it has been shown that the mentioned carcinogens can be formed in the human gastrointestinal tract only under certain conditions - malnutrition, a decrease in the acidity of the gastric juice, the appearance abnormal microflora, etc. Elimination of digestive disorders makes the risk of cancer under the influence of nitrates and nitrites minimal.
It has been established that the chemical substances (aniline, ethanolamine) present in the objects surrounding the human environment increase the carcinogenic effect of the azo compounds and cause liver cancer in an animal experiment.
Epidemiological studies have revealed a number of factors indicative of the possibility of developing cancer when using vegetables and fruits grown in pesticide use conditions. It has been established that the number of oncological patients in the local rural population increases statistically with the increase in the area of fields treated with herbicides. It was found out that in families where children developed brain tumors, insecticides were used (up to 80% of families) for the sanitation of domestic animals, especially if this coincided with the first 6 months of the life of the newborn.
According to the latest WHO classification, carcinogenicity for humans is arsenic and its compounds, chromium and some of its compounds, and the technological processes of nickel refining are also dangerous. To the group of substances with a high degree of probability of carcinogenic activity for people belong cadmium and nickel and some of their compounds. Finally, there is evidence of a carcinogenic activity for beryllium and some of its compounds.
Studies have shown that in Tatarstan the high incidence of colon cancer is correlated with the increase in strontium, lead and cadmium in the soil and vegetative layer, and the rectum with chromium, lead, strontium and cadmium.
All metals in the form of minerals in one or another quantity are present in the human environment. In the form of various compounds, metals can enter the atmosphere. They are sources of high-temperature processing of natural materials containing these metals: ore melting, glass production, burning of coal, production of pesticides, etc.
Some studies indicate an increased risk of developing colon cancer when eating dirty water, and bladder tumors with chlorinated water. It has been established that in the course of water treatment (principally using chlorine as a disinfectant) fundamentally new chemical compounds are formed, most of which are capable of inducing mutations and malignant neoplasms.
Recently, one more physical factor of the human environment is beginning to attract attention from the point of view of potential oncological danger. We are talking about magnetic fields. With the development of scientific and technical progress, the probability of influencing people's variables and permanent magnetic fields increases. Meanwhile already now there are data on the basis of which it is possible at least to suspect the carcinogenic effect of such influences on people. To date, mechanisms have not been fully defined through which low-frequency fields can influence the development of cancer or other pathology. At the same time, there are data confirming the hypothesis that the exposure of electromagnetic fields is related to the incidence of leukemia in children.
Hereditary cancer
The share of inherited forms of cancer, according to various estimates, is from 2.3 to 7.0% of all malignant diseases. The emergence of "hereditary tumors" is associated with mutations in the sex cells.
Despite the genetic nature of all types of cancer, not all of them are hereditary diseases, since in most cases they are associated with somatic mutations that are not inherited.
According to the nature of the inherited trait, hereditary forms of cancer include the following groups:
- inheritance of a gene that causes a certain form of cancer (eg, Wilms' tumor, hereditary retinoblastoma);
- inheritance of a gene that increases the risk of cancer, - hereditary predisposition to cancer (eg, pigment xeroderma);
- polygenic inheritance - a tumor or a predisposition to it occurs when a patient has several hereditary signs (for example, collagenoses).
Family polyposis of the intestine
Multiple adenomas of the colon in the form of polyps. By the age of 40, in 100% of cases, colon carcinoma develops. The inheritance is autosomal dominant.
Gardner's syndrome (hereditary adenomatosis)
The disease manifests itself at the age of 20 to 30 years with polyps of the colon, atheromas, leiomyomas and dermoid cysts of the skin, skull osteomas. Polyps of the intestine are always malignant.
The Peitz-Turena-Jegers syndrome
Simultaneous lesion of the intestine (polyposis with dyspeptic disorders) and skin (pigmentation disorder). Adenomas of the intestine are malignant in 5% of cases.
Wilms tumor (nephroblastoma, embryonic kidney cancer)
It accounts for about 20% of all cancers in children. It occurs when the development of the kidney at any age, but more often about 3 years. Inherited more than 30% of cases of tumors.
Mammary cancer
Approximately 5 to 10% of cases of breast cancer are hereditary, their share is due to the vertical transmission of the BRCA1 and BRCA2 genes mutated. Hereditary form of breast cancer is more often diagnosed in young women of reproductive age. The risk of developing cancer is 2 to 3 times higher in women whose relatives have had breast cancer. An increased risk of developing malignant breast tumors is transmitted from parents to children.
Ovarian Cancer
From 5 to 10% of cases of ovarian cancer are hereditary, about 10% of all malignant melanomas are inherited by autosomal dominant type. The proportion of hereditary forms of stomach cancer is low. The probability of developing carcinoma of the stomach in children or brothers and sisters of the patient is 2-3 times higher than the risk in the general population. Great importance is given to genetic factors in the formation of primary-multiple malignant neoplasms.