Why do we have cancer

Cancer is a group of diseases that cause abnormal cell growth and have the ability to attack other parts of the body. Formerly a rather rare cause, today it counts for more than 15 % of deaths. Why are there so many cases of cancer today and how can we avoid it by our own choice in most cases?

Cancer is caused by a random change in the genome of a replicable cell that leads to uncontrolled growth and tumor formation. A change in the genome can be caused either by a mutation, when part of the genetic information is changed, or by its damage. The damaged genome is trying to repair the cell. If the damage is worse than the cell's ability to repair, it can lead to apoptosis, controlled cell death. If apoptosis or DNA repair is not successful, subsequent random processes can stimulate uncontrolled growth and cancer. In a natural way, up to tens of thousands of single cell damage occurs daily. By our own behavior and lifestyle, we can increase the number of damages.^[1]

Risk factors for cancer include smoking, obesity, poor diet, low physical activity, high alcohol consumption, certain infectious diseases, exposure to radiation and chemicals that pollute the environment, and congenital defects in genetic information. The risk of developing cancer increases further if the individual is affected by certain diseases, and as well with age.^[2]

Smoking is one of the biggest causes of cancer. In developed countries, the risk of cancer caused by smoking accounts for up to 30 % of all cases and accounts for 90 % of lung cancer cases. Smoking also causes cancer of the larynx, head, neck, stomach, bladder, kidney, esophagus and pancreas. Tobacco smoke contains over 40 carcinogenic substances that have the ability to damage cell DNA and thus increase the risk of cancer. In addition to cancer itself, smoking causes a number of other diseases.^[3]

Obesity affects up to 12 % of the world's population and, in addition to many other diseases, is also at high risk of cancer. Obesity increases the risk of cancer of the esophagus, pancreas, intestines, breast, inner lining of the uterus, kidneys, thyroid, liver, and gallbladder. The exact effect of obesity on cancer development is not fully understood, but it is thought that an environment full of fat cells causes inflammation that damages DNA in the long run, the repair of which increases the risk.^[4]

Poor eating also contributes to the risk of cancer, especially with regard to the specific substances we get into our body. High salt intake is behind gastric cancer.^[5] Aflatoxin B1, found in improperly stored and processed peanuts, corn, and similar foods, can cause liver cancer.^[6] Red meat and processed meat (bacon, ham, salami, etc.) also carry an increased risk of bowel cancer in particular.^[7] Overeating also affects the development of cancer.

Low physical activity is often responsible for obesity, which poses a high risk of cancer, but also reduces the efficiency of the immune and endocrine systems, increases the levels of sex hormones and insulin, or, for example, slows the flow of food through the digestive system.^[8]

High alcohol consumption accounts for more than 3 % of cancers of the breast, mouth, esophagus, pharynx, larynx, intestines, liver, stomach, and ovaries. Tissue with which alcohol is in direct contact after ingestion is affected by ethanol, which kills the cells with which it is in contact. The surrounding stem cells divide when trying to replace dead cells, increasing the risk of error and cancer. In organs that are not in direct contact with ethanol, acetaldehyde, which is formed by the metabolism of ethanol in the liver, does the job.^[9]

Infections involved in the development of cancer have the ability to alter genetic information within a cell. Accidental processes can lead to a mutation that leads to carcinogenic growth. In developed countries, this is a rather marginal cause, but in developing countries, infectious diseases account for up to 15 % of cancer. The most common infectious diseases in this group include Helicobacter pylori due to gastric adenocarcinoma or gastric lymphomas, hepatitis B and C causing liver cancer, human papillomavirus causes genital, oral, and pharyngeal cancer, Epstein-Barr virus causes many types of lymphoma, and HIV.^[10]

High-energy radiation has the ability to directly damage DNA.^[11] In addition to medical devices such as X-rays, computed tomography (CT) or positron emission tomography (PET), this category also includes exposure to UV radiation, flying and long-term exposure to accumulated radon. UV radiation is responsible for most cases of skin cancer.^[12] Melanoma is a cancer of pigment cells and is mainly caused by UV radiation from the sun and solar lamps. People with many freckles and a weak immune system are more prone to this disease. Melanoma is the less common and most dangerous type of skin cancer.^[13] Other types of skin cancer are easier to treat and have a low chance of spreading to other parts of the body.

Some environmental pollutants cause cancer through their structure, most often in the form of very thin needles. The best known example is inhaled asbestos, which was used as an insulation material in buildings until the 1980s.^[14] This category also includes powdered cobalt, nickel, silica, arsenic and many others.^[15]

Although more than 50 types of inherited cancers are known, genome defects in transmission from parent to child account for only about 3 to 10 % of cases. These defects are caused, for example, by an inherited deficiency of some enzymes responsible for repairing damaged DNA or regulating cell growth. Accumulating DNA damage causes premature aging and increases the risk of cancer. Some specific types of mutations also carry an increased risk of breast, ovarian and colon cancers. An increased risk of cancer due to genetic influence may be revealed by testing.^[16]

The risk of cancer can be significantly reduced by proper behavior of the individual, such as avoiding cigarette smoking (even passive smoking), maintaining a healthy body weight, significantly reducing alcohol consumption, including large amounts of fruits, vegetables and whole grains in the diet, vaccination against certain infectious disease, the reduction of highly processed food and red meat, and the avoidance of excessive exposure to sunlight or the consistent use of high-factor sunscreen. With the right behavior, it is possible to avoid up to one third of all cancers worldwide, in developed countries it is even as high as 80 %.^[17]