Causes of cancer

WHO identifies the following main causes of cancer: nutrition (35%), smoking (30%), sexual relations, reproduction (10%), insolation (5%), ionizing radiation (3.5%), occupational hazards (3.5%), environmental pollution (3.5%), alcohol abuse (2.7%), heredity (2.3%).

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Diet as a Cause of Cancer

Excess of any of the main food ingredients - proteins, fats and carbohydrates - in the diet contributes to 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 the caloric content of the diet, the consumption of easily digestible carbohydrates. An increase in animal proteins in the diet above the norm also increases the incidence of cancer, which is largely due to the influence of animal fat and cholesterol.

Eating salted meat, especially in combination with smoking, is considered the main risk factor for laryngeal cancer. A link has been found between the amount of sugar in the diet and the incidence of breast cancer. An inverse correlation has been established between starch consumption and the incidence of colon cancer. Starch is a good substrate for the production of butyrate, which has a protective effect on the epithelium of the colon. Micronutrients contained in canned foods (salt, nitrites) and phosphates damage the mucous membrane in the digestive tract, which increases the possibility of mutagenic effects.

Protective factors include calcium, which reduces the permeability of the mucous membrane, and antioxidants (vitamin C, carotenoids), trace elements (selenium) and plant anticarcinogens (phytoestrogens, flavonoids, tea polyphenols).

Epidemiological studies show that excess fat in the diet (both plant and animal origin) promotes cancer development. The factors of procarcinogenic action of fat are as follows:

• influence on the metabolism of carcinogens (including on the intestinal microflora, which is believed to increase the conversion of bile acids into carcinogenic metabolites);
• direct action on the tissues in which the tumor develops;
• effect on the endocrine system;
• influence on the immune and hemocoagulation systems.

Excess body weight increases the risk of developing almost all forms of cancer, and the more it is, the higher the danger. The scientific literature has accumulated a lot of data confirming the connection between obesity and the development of cancer of the kidney, colon, lungs, mammary glands and female genital area.

In severe obesity, the risk of dying from cancer is 52% higher in men and 62% higher in women compared to people with normal body weight.

A study conducted in the United States found that among women with the highest body weight, uterine cancer was 6 times more common, kidney cancer 5 times more common, cervical cancer 3 times more common, and breast, gallbladder, pancreas, and esophagus cancer 2 times more common than in control groups.

Among men with the highest body weight, liver cancer was the cause of death 6 times more often, pancreatic cancer 2 times more often, gallbladder, stomach and rectum cancer 75% more often compared to the control groups.

In recent years, considerable attention has been paid to the possible protective role of so-called plant fibers, which include cellulose, pectin, etc. It is believed that food containing plant fibers (in particular, cabbage, peas, beans, carrots, cucumbers, apples, plums, etc.) can help reduce the incidence of gastrointestinal cancer. It has not yet been determined whether the protective property of dietary fiber is associated with its quantity or with the function of certain components. Dietary fiber affects the fermentation process in the colon (ending in the production of short-chain fatty acids such as butyrate, an apoptosis inhibitor) and increases the volume of fecal matter (thus leading to a decrease in the concentration of carcinogenic substances in the lumen of the colon).

Some plant components, primarily lignin-containing, can increase estrogen levels in the body as a result of metabolism in the intestine. Soy is one of these plants.

The most favorable effect of a rational lifestyle was noted among non-smokers who do not drink alcohol or meat and eat fresh vegetables daily. In this group of people, the annual mortality from tumors in standardized indicators was 324 cases per 100 thousand people compared to 800 cases per 100 thousand people among people with an opposite lifestyle. At the same time, protein starvation contributes to a significant decrease in immune activity and is also very undesirable.

Causes of cancer: smoking

According to experts of the WHO Committee on Smoking Control, there is currently convincing evidence of a cause-and-effect relationship between smoking and lung cancer. It is based on numerous retrospective studies conducted in a number of countries. These studies invariably reveal a close connection between lung cancer and cigarette consumption. At the same time, the degree of risk of developing lung cancer is directly dependent on the number of cigarettes smoked, the age at which smoking was started, the frequency and depth of inhalation, 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 two packs of cigarettes or more per day have a 24 times higher risk of developing lung cancer than non-smokers.

Smoking and alcohol consumption are the leading risk factors for cancers of the head, neck, and mouth, including cancers of the lip, tongue, gums, larynx, and pharynx. Approximately 400,000 new cases of these diseases are diagnosed worldwide each year, and most of them occur in developing countries. Researchers have found that tobacco smoke destroys antioxidant molecules in saliva, turning it into a mixture of dangerous chemicals. Arsenic, nickel, cadmium, and beryllium, which are present in cigarette tobacco, can (up to 10% for some) pass into tobacco smoke when smoking. When saliva is exposed to tobacco smoke, it not only loses its protective properties, but even becomes dangerous and contributes to the destruction of cells in the oral cavity.

Smoking also increases the incidence of cancer of the esophagus, gallbladder, and pancreas. Published prospective studies conducted in the United States have established a link between smoking and the risk of developing pancreatic cancer. A two- to three-fold increase in the risk of developing pancreatic cancer was shown in smokers compared to nonsmokers.

The mechanism by which smoking affects cancer incidence is unknown. It is believed that specific carcinogens enter the pancreas either hematogenously or through bile reflux. Stopping smoking can prevent 25% of pancreatic cancer deaths.

There are a large number of publications indicating the carcinogenic effect of alcohol in the development of cancer of the upper gastrointestinal tract, primary liver cancer, breast cancer, rectal cancer, etc.

Despite the impressive amount of scientific information confirming the carcinogenicity of alcohol consumption for humans, the mechanism of the carcinogenic effect of alcohol is still unclear. According to experimental studies, ethanol as such is not carcinogenic. It is believed that ethanol plays the role of a promoter of carcinogenesis.

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Reproductive history

This factor plays an important role in the etiology of tumors of the female genital organs. These are, first of all, the features of the menstrual, sexual, reproductive and lactation functions. Thus, early age of onset of menstruation (menarche) and late menopause increase the risk of developing breast cancer, cancer of the uterine body and ovary. In women whose age of menarche was 15 years or older, compared with women who began menstruating before 13, the oncological risk of breast cancer is reduced by half. In women with late menopause (54 years or older), the oncological risk is increased by 4 times compared with women whose menopause occurred before 47 years. Childbirth reduces the risk of developing breast cancer. Compared with a woman who has never given birth, a woman who has given birth to one child has an oncological risk reduced by 50%. Moreover, with the increase in the number of pregnancies ending in childbirth, the risk of developing breast cancer continues to decrease, and a woman who has given birth to three or more children has a 65% lower risk than women who have never given birth. Early childbirth is also a factor that reduces the risk of developing breast cancer. Thus, women who gave birth to their first child before the age of 25 have a 35% lower cancer risk than women who gave birth to their first child after the age of 35.

Causes of cancer: ionizing radiation, insolation

Ionizing radiation found in the human habitat consists of natural (environmental) background radiation and ionizing sources, the origin of which is due to human activity.

The radiation (ionizing) natural background consists of three types of ionizing radiation sources. The first of these are cosmic rays reaching the Earth's surface, the second is the radiation of radioactive elements that are part of the Earth's crust (soil, rocks, sea water, and in some cases, groundwater). The presence of radioactive elements in rocks results in their presence in building materials and ionizing radiation from stone buildings. Radon, a radioactive gas, is slowly released in varying quantities from rocks and from building materials obtained from them. It is also released from structural elements of stone buildings. These circumstances determine the presence of radon in sea water and the waters of some springs, as well as in industrial and residential premises. Finally, the third type is the ionizing radiation of radioactive nuclides that are part of the human (and animal) body. What is interesting is that each of these three types of sources of ionizing radiation currently makes approximately the same contribution to the overall level of natural background radiation.

The total radiation load on a person in modern society, according to existing estimates, is determined approximately by 2/3 by the action of the natural background of ionizing radiation and by 1/3 by the influence of its anthropogenic sources. Among the latter, the largest share is the use of ionizing radiation in medicine (diagnostics and therapy). The radiation load of this origin reaches approximately 30% of the total load on a person of ionizing radiation from all possible sources. The radiation load from other sources of anthropogenic origin, including radioactive atmospheric precipitation, professional radiation hazards and radioactive waste, is only a few percent (about 2%) of the total load occurring from all sources.

According to estimates by radiation hygiene specialists, the combined carcinogenic effects of ionizing radiation account for only about 1–10% of all malignant tumors in humans.

An analysis of leukemia cases in Greece since 1980 has shown that the incidence of the disease in children under 12 months of age among those exposed in utero to radiation from the Chernobyl fallout is 2.6 times higher than in those not exposed.

The impact of low doses of radiation on the thyroid gland of children is the cause of a sharp increase in the incidence of papillary forms of thyroid cancer. The peak of their occurrence is observed in the 20-25-year period after radiation exposure in doses of 10-60 Gy.

The second important radiation carcinogenic factor of the human environment is solar ultraviolet radiation. Based on epidemiological studies, it has been concluded that the overwhelming majority of various forms of skin cancer should be considered as a geographic pathology associated with long-term excessive exposure to solar ultraviolet rays. Solar ultraviolet rays are also of important etiological significance for lip cancer and malignant melanoma of the skin.

Activation of the proto-oncogene is caused by ultraviolet radiation with a wavelength of 160 - 320 nm, which is absorbed by DNA with the transition of its bases to 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 ones, ultraviolet quanta suppress the immune and reparative systems of the body.

It is known that as a result of anthropogenic impacts on the stratosphere, the thickness of its ozone layer may decrease, which leads to an increase in the flow of ultraviolet rays reaching the human habitat. Meanwhile, an increase in the intensity of ultraviolet radiation from the Sun by 1% increases the incidence of skin cancer by 2%.

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Environmental Pollution as a Cause of Cancer

The increase in malignant neoplasms is now believed to be due to the increased level of environmental pollution by various chemical and physical agents with carcinogenic properties. It is generally accepted that up to 85-90% of all cancer cases are caused by environmental carcinogens. Of these, about 80% are chemical carcinogens, primarily polyaromatic hydrocarbons (PAH) and nitrosamines (NA). Systematic studies of the level of PAH pollution in natural environments have revealed a global distribution pattern. It has been established that the concentration of PAH, primarily benz(a)pyrene, in the environment is related to blastomogenic exposure.

Currently, the increasing general pollution of soil and water bodies with nitrites and nitrates, in particular due to the increased use of nitrogen-containing fertilizers, is of great concern. It causes these agents to appear in plants and plant-based foods, feed and even livestock products, such as milk.

An important aspect of this problem is that nitroso compounds can be formed 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 (nitrite) pollution still remains relevant for some European countries, but research has shown that the aforementioned carcinogens can form in the human gastrointestinal tract only under certain conditions - poor nutrition, decreased acidity of gastric juice, the appearance of 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 chemicals (aniline, ethanolamine) present in objects in the human environment enhance the carcinogenic effect of azo compounds and cause liver cancer in animal experiments.

Epidemiological studies have revealed a number of factors indicating the possibility of developing cancer when consuming vegetables and fruits grown under conditions of pesticide use. It has been established that with an increase in the area of fields treated with herbicides, the number of cancer patients in the local rural population statistically significantly increases. It has been found that in families in which children developed brain tumors, insecticides were used (up to 80% of families) to sanitize domestic animals, especially if this coincided with the first 6 months of life of newborns.

According to the latest WHO classification, arsenic and its compounds, chromium and some of its compounds have been reliably proven to be carcinogenic to humans; nickel refining processes are also dangerous. Cadmium and nickel and some of their compounds belong to the group of substances with a high probability of carcinogenic activity for humans. Finally, there is data on the carcinogenic activity of beryllium and some of its compounds for humans.

As studies have shown, in Tatarstan, the high incidence of colon cancer correlates with an increase in the content of strontium, lead and cadmium in the soil and plant layer, and in the rectum - with chromium, lead, strontium and cadmium.

All metals in the form of minerals are present in varying quantities in the environment around humans. In the form of various compounds, metals can enter the atmosphere. Their sources are high-temperature processes of processing natural materials containing these metals: smelting of ores, glass production, burning of coal, production of pesticides, etc.

Some studies indicate an increased risk of developing rectal cancer when drinking dirty water, and bladder tumors when drinking chlorinated water. It has been established that the process of water treatment (mainly when using chlorine as a disinfectant) produces fundamentally new chemical compounds, most of which are capable of inducing mutations and malignant neoplasms.

Recently, another physical factor of the human environment has begun to attract attention from the point of view of potential oncological danger. We are talking about magnetic fields. With the development of scientific and technological progress, the probability of exposure of people to variable and constant magnetic fields increases. Meanwhile, there is already data on the basis of which one can at least suspect a carcinogenic effect of such exposure on people. To date, the mechanisms through which low-frequency fields can influence the development of cancer or other pathology have not been fully determined. At the same time, there is data confirming the hypothesis of a connection between exposure to electromagnetic fields and the incidence of leukemia in children.

Hereditary cancer

The share of hereditary forms of cancer, according to various estimates, is from 2.3 to 7.0% of all malignant diseases. The occurrence of "hereditary tumors" is associated with mutations in germ 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:

• inheriting a gene that causes a certain form of cancer (eg, Wilms tumor; hereditary retinoblastoma);
• inheriting a gene that increases the risk of cancer - a hereditary predisposition to cancer (eg, xeroderma pigmentosum);
• polygenic inheritance - a tumor or a predisposition to it occurs when a patient has a combination of several hereditary traits (for example, collagenoses).

Familial intestinal polyposis

Multiple colon adenomas in the form of polyps. By the age of 40, colon carcinoma develops in 100% of cases. Inheritance is autosomal dominant.

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Gardner's syndrome (hereditary adenomatosis)

The disease manifests itself at the age of 20-30 years with colon polyps, atheromas, leiomyomas and dermoid cysts of the skin, osteomas of the skull. Intestinal polyps always become malignant.

Peutz-Touraine-Jeghers syndrome

Simultaneous damage to the intestines (polyposis with dyspeptic disorders) and skin (pigmentation disorders). Intestinal adenomas become malignant in 5% of cases.

Wilms tumor (nephroblastoma, embryonal kidney cancer)

It accounts for about 20% of all types of cancer in children. It occurs when the kidney is not developing properly at any age, but most often around 3 years of age. More than 30% of tumors are hereditary.

Breast cancer

Approximately 5-10% of breast cancer cases are hereditary, their share is due to vertical transmission of mutated BRCA1 and BRCA2 genes. Hereditary breast cancer is most often diagnosed in young women of reproductive age. The risk of developing cancer is 2-3 times higher in women whose relatives had breast cancer. The increased risk of developing malignant breast tumors is passed from parents to children.

Ovarian cancer

From 5 to 10% of ovarian cancer cases are hereditary forms, about 10% of all malignant melanomas are inherited in an autosomal dominant manner. The proportion of hereditary forms of stomach cancer is small. The probability of developing stomach carcinoma in children or siblings of a patient is 2 to 3 times higher than the risk in the general population. Great importance is attached to genetic factors in the formation of primary multiple malignant neoplasms.