Cancer is a disease caused by genetic changes leading to uncontrolled cell growth and tumor formation. The basic causes of sporadic (non-familial) cancer are DNA damage and genomic instability. A small percentage of cancers are caused by inherited genetic mutations. Most cancers are associated with environmental, lifestyle, or behavioral exposure. Cancer is generally not contagious in humans, although it can be caused by oncovirus and cancerous bacteria. The term "environment", as used by cancer researchers, refers to anything outside the body that interacts with humans. The environment is not limited to the biophysical environment (eg exposure to factors such as air pollution or sunlight), but also includes lifestyle and behavioral factors. More than a third of cancer deaths worldwide (and about 75-80% in the United States) are potentially avoided by reducing exposure to known factors. Common environmental factors that contribute to cancer deaths include exposure to different chemicals and physical (tobacco use accounts for 25-30% of cancer deaths), environmental pollutants, diet and obesity (30-35%), infections (15-20%), and radiation (both ionizing and non-ionizing, up to 10%). These factors act, at least in part, by altering the function of genes within the cell. Usually many such genetic changes are needed before the cancer develops. Aging has been repeatedly and consistently considered an important aspect to consider when evaluating risk factors for the development of certain cancers. Many of the molecular and cellular changes involved in cancer development accumulate during the aging process and eventually manifest as cancer.
Video Causes of cancer
Heredity
Although there are more than 50 identifiable types of hereditary cancers, less than 0.3% of the population are carriers of cancer-related genetic mutations and this makes up less than 3-10% of all cancer cases. Most cancers are non-hereditary ("sporadic cancer"). Hereditary cancer is primarily caused by congenital genetic disorders. The cancer syndrome or family cancer syndrome is a genetic disorder in which inherited genetic mutations in one or more genes affect the affected individual for cancer progression and may also cause early onset of this cancer. Although cancer syndrome shows an increased risk of cancer, the risks vary. For some of these diseases, cancer is not a major feature and is a rare consequence.
Many of these syndromes are caused by mutations in tumor suppressor genes that regulate cell growth. Other common mutations alter the function of DNA repair genes, oncogenes and genes involved in the production of blood vessels. Some inherited mutations in the BRCA1 and BRCA2 genes with over 75% risk of breast cancer and ovarian cancer. Some of the congenital genetic disorders that can cause colorectal cancer include familial adenomatous polyposis and non hereditary colon cancer; However, this represents less than 5% of cases of colon cancer. In many cases, genetic testing can be used to identify mutated genes or chromosomes passed from generation to generation.
Examples of cancer syndrome
- Ataxia telangiectasia
- Bloom Syndrome
- BRCA1 & amp; BRCA2
- Fanconi Anemia
- Familial adenomatous polyposis
- Hereditary breasts and ovarian cancer
- Hereditary hereditary colon cancer
- Li-Fraumeni Syndrome
- Nevoid basal cell carcinoma syndrome
- Von Hippel-Lindau's Disease
- Werner's syndrome
- Xeroderma pigmentosum
Maps Causes of cancer
Physical and chemical agents
Certain substances, known as carcinogens, have been linked to certain types of cancer. Common examples of non-radioactive carcinogens are inhaled asbestos, certain dioxins, and tobacco smoke. Although society generally associates carcinogenicity with synthetic chemicals, it is equally likely to arise in both natural and synthetic substances. It is estimated that about 20,000 cancer deaths and 40,000 new cases of cancer each year in the US are caused by work. Every year, at least 200,000 people die worldwide due to cancers associated with their workplace. Millions of workers are at risk of developing cancer such as lung cancer and mesothelioma from inhaling asbestos fibers and tobacco smoke, or leukemia from benzene exposure in their workplace. Cancer associated with a person's job is believed to represent between 2-20% of all cases. Most deaths from cancer caused by occupational risk factors occur in developed countries. Work stress is not a significant factor at least in lung, colorectal, breast and prostate cancers.
Smoking
Tobacco smoking is associated with many forms of cancer, and causes 80% of lung cancers. Decades of research have shown a link between tobacco use and cancer in the lungs, larynx, head, neck, stomach, bladder, kidney, esophagus, and pancreas. There is some evidence showing a slightly increased risk of developing myeloid leukemia, squamous cell sinonasal cancer, liver cancer, colorectal cancer, gallbladder cancer, adrenal glands, small intestine, and various cancers in childhood. Tobacco smoke contains more than fifty known carcinogens, including nitrosamines and polycyclic aromatic hydrocarbons. Tobacco is responsible for about one in three cancer deaths in developed countries, and about one in five worldwide. The mortality rate of lung cancer in the United States has reflected the smoking pattern, with the increase in smoking followed by a dramatic increase in lung cancer mortality rates and, more recently, a decrease in smoking rates since the 1950s followed by a decrease in lung cancer mortality rates men since 1990 However, the number of smokers worldwide is still on the rise, leading to what some organizations describe as tobacco epidemics.
Electronic cigarettes or e-cigarettes are handheld electronic devices that simulate tobacco smoke. Long-term use of high voltage electronic cigarettes (5.0 V) daily can produce formalin formalin chemicals at a greater rate than smoking, which is considered a lifetime cancer risk of 5 to 15 times greater than smoking. However, the overall safety and long-term health effects of electronic cigarettes remain uncertain.
Materials
Some substances cause cancer mainly through their physical, not chemical, effects on cells. A striking example of this is the prolonged exposure to asbestos, the natural mineral fiber that is the main cause of mesothelioma, which is a cancer of the serous membrane, usually a serous membrane that surrounds the lungs. Other substances in this category, including synthetic fibers such as wollastonite fibers, attapulgite, glass wool, and woolen wool, are believed to have a similar effect. Non-fibrous particle materials that cause cancer include cobalt powder and metal nickel, and crystalline silica (quartz, cristobalite, and tridim). Usually, physical carcinogens must enter the body (such as through inhaling small pieces) and require years of exposure to develop cancer. Common occupational carcinogens include:
- arsenic
- asbestos
- benzene
- beryllium
- cadmium
- chromium
- ethylene oxide
- nickel
- radon
- vinyl chloride
- radium
- plutonium
Lifestyle
Many different lifestyle factors contribute to an increased risk of cancer. Together, diet and obesity are associated with about 30-35% of cancer deaths. Dietary recommendations for cancer prevention usually include emphasis on vegetables, fruits, grains, and fish, and avoiding processed meats, red meat, animal fats, and refined carbohydrates. The evidence to support dietary changes is not definitive.
Alcohol
Alcohol is an example of chemical carcinogens. The World Health Organization has classified alcohol as a Group 1 carcinogen. In Western Europe 10% of cancers in males and 3% of cancer in women are associated with alcohol. Worldwide, 3.6% of all cancer cases and 3.5% of cancer deaths are caused by alcohol. In particular, the use of alcohol has been shown to increase the risk of developing cancer of the mouth, esophagus, pharynx, larynx, stomach, liver, ovaries, and colon. The main mechanisms of cancer development involve increased exposure to acetaldehyde, carcinogenic products and ethanol breakdown. Other mechanisms have been proposed, including alcohol-related nutritional deficiencies, changes in DNA methylation, and induction of oxidative stress in tissues.
Diet
Certain foods have been linked to certain cancers. Research shows that people who eat red or processed meat have a higher risk of breast cancer, prostate cancer, and pancreatic cancer. This may be partly explained by the presence of carcinogens in foods cooked at high temperatures. Some risk factors for the development of colorectal cancer include high intake of fat, alcohol, red and processed meats, obesity, and lack of physical exercise. High salt diet associated with stomach cancer. Aflatoxin B1, a food that often contaminates, is associated with liver cancer. Chewing betel has been shown to cause oral cancer.
The relationship between diet and the development of certain cancers can partly explain the difference in cancer incidence in various countries. For example, gastric cancer is more common in Japan because the frequency of high-salt diet and colon cancer is more common in the United States due to increased intake of processed meats and red meat. The immigrant community tends to develop a cancer risk profile in their new country, often within one to two generations, indicating a substantial link between diet and cancer.
Obesity
In the United States, overweight is associated with the development of many types of cancer and is a factor in 14-20% of all cancer deaths. Every year, nearly 85,000 new cancer diagnoses in the United States are associated with obesity. Individuals who undergo bariatric surgery to lose weight have reduced the incidence of cancer and death.
There is a link between obesity and colon cancer, post-menopausal breast cancer, endometrial cancer, kidney cancer, and esophageal cancer. Obesity is also associated with the development of liver cancer. The current understanding of the mechanisms of cancer development in obesity is associated with abnormal levels of protein metabolism (including growth factors such as insulin) and sex hormones (estrogen, androgen and progestogen). Adipose tissue also creates an inflammatory environment that can contribute to the development of cancer.
Physical inactivity is believed to contribute to cancer risk not only through its effects on weight but also through negative effects on the immune system and endocrine system. More than half the effects of the diet are due to overnutrition rather than eating too little healthy food.
Hormones
Some hormones play a role in the development of cancer by promoting cell proliferation. Growth factors such as insulin and its binding proteins play a key role in cancer cell growth, differentiation and apoptosis, suggesting a possible involvement in carcinogenesis.
Hormones are important agents in sex-related cancers such as breast, endometrial, prostate, ovarian, and testicular cancers, as well as thyroid and bone cancer. For example, female girls with breast cancer have significantly higher levels of estrogen and progesterone than girls without breast cancer. This higher level of hormones may explain why this woman has a higher risk of breast cancer, even in the absence of breast cancer genes. Likewise, African men have higher testosterone levels than men of European descent, and have higher rates of prostate cancer. Asian ancestral men, with the lowest levels of testosterone-activated androstanediol glucuronide, had the lowest rates of prostate cancer.
Other factors are also relevant: obese people have higher levels of hormones associated with cancer and higher cancer rates. Women who use hormone replacement therapy have a higher risk of cancer associated with the hormone. On the other hand, people who exercise far more than average have lower hormone levels, and lower cancer risk. Osteosarcoma can be promoted by growth hormone.
Some treatments and preventive approaches take advantage of this cause by artificially reducing hormone levels, and thus discouraging hormone-sensitive cancers. Because steroid hormones are powerful movers of gene expression in certain cancer cells, altering the level or activity of certain hormones can cause certain cancers to stop growing or even experience cell death. Perhaps the best known example of hormonal therapy in oncology is the use of a tamoxifen selective estrogen receptor modulator for the treatment of breast cancer. Another class of hormonal agents, aromatase inhibitors, now has a growing role in the treatment of breast cancer.
Infection and inflammation
Worldwide, about 18% of cancer cases are linked to infectious diseases. This proportion varies in different regions of the world from 25% in Africa to less than 10% in developed countries. Viruses are the usual infection agents that cause cancer but bacteria and parasites also contribute. Infectious organisms that increase the risk of cancer are often sources of DNA damage or genomic instability.
Virus
Viral infection is a major risk factor for cervical and liver cancer. The virus that causes cancer is called oncovirus . These include human papillomavirus, Epstein-Barr virus (B-cell lymphoproliferative disease and nasopharyngeal carcinoma), Kaposi's sarcoma sarcoma (Kaposi's sarcoma and primary effusion lymphoma), hepatitis B and hepatitis C virus (hepatocellular cancer), and Human -cell leukemia virus-1 (T cell leukemia).
In Western developed countries, human papillomavirus (HPV), hepatitis B virus (HBV) and hepatitis C virus (HCV) are the most common oncovirus. In the United States, HPV causes most cervical cancers, as well as some cancers of the vagina, vulva, penis, anus, rectum, throat, tongue, and tonsils. Among high risk HPV viruses, HPV E6 and E7 oncoproteins inactivate tumor suppressor genes when they infect cells. In addition, oncoprotein independently induces genomic instability in normal human cells, leading to an increased risk of developing cancer. Individuals with chronic hepatitis B virus infection are more than 200 times more likely to develop liver cancer than uninfected people. Cirrhosis of the liver, whether from chronic viral hepatitis infection or alcohol abuse, is independently associated with the development of liver cancer, but the combination of cirrhosis and viral hepatitis shows the highest risk of developing liver cancer.
Bacteria and parasites
Certain bacterial infections also increase the risk of cancer, as seen in Helicobacter pylori-induced gastric carcinoma. The mechanism by which H. pylori causes cancer may involve chronic inflammation or direct action of some bacterial virulence factors. Parasitic infections strongly associated with cancer include Schistosoma haematobium (squamous cell carcinoma of the bladder) and liverworm, Opisthorchis viverrini and Clonorchis sinensis (cholangiocarcinoma) ). Inflammation triggered by a worm's egg appears to be a cancer-causing mechanism. Certain parasitic infections may also increase the presence of carcinogenic compounds in the body, leading to the development of cancer. Tuberculosis infection, caused by mycobacterium M. tuberculosis , is also associated with the development of lung cancer.
Inflammation
There is evidence that inflammation itself plays an important role in the development and development of cancer. Chronic inflammation can lead to DNA damage over time and the accumulation of random genetic changes in cancer cells. Inflammation can contribute to proliferation, survival, angiogensis and migration of cancer cells by affecting the tumor microenvironment. Individuals with inflammatory bowel disease are at an increased risk of developing colorectal cancer.
Radiation
Up to 10% of invasive cancers are associated with radiation exposure, including non-ionizing radiation and ionizing radiation. Unlike chemical or physical triggers for cancer, ionizing radiation hits molecules in cells at random. If it happens to attack the chromosome, it can break down the chromosomes, produce abnormal chromosome numbers, disable one or more genes on the part of the chromosome it beats, remove parts of the DNA sequence, cause chromosomal translocation, or cause other types of chromosomal abnormalities. Large damage usually results in cell death, but smaller damage can leave a stable, functional cell that may be able to multiply and develop into cancer, especially if the tumor suppressor gene is damaged by radiation. The three independent stages seem to be involved in the creation of cancer by ionizing radiation: morphological changes to cells, acquiring cellular immortality (normal loss, limiting cell-limiting processes), and adaptations that support tumor formation. Even if the radiation particles do not attack the DNA directly, it triggers a response from a cell that indirectly increases the likelihood of mutation.
Non-ionizing radiation
Not all types of electromagnetic radiation are carcinogenic. Low-energy waves in the electromagnetic spectrum including radio waves, microwaves, infrared radiation, and visible light are considered not because they do not have enough energy to break the chemical bond. Non-ionizing radio frequency radiation from cell phones, power transmissions, and other similar sources has been described as a possible carcinogen by the International Agency for International Cancer Research of the World Health Organization. However, studies have not found a consistent relationship between cell phone radiation and cancer risk.
High-energy radiation, including ultraviolet radiation (present in the sun), x-rays, and gamma radiation, are generally carcinogenic, if received in sufficient doses. Prolonged exposure to ultraviolet radiation from the sun can cause melanoma and other skin malignancies. Most non-invasive cancers are non-melanoma skin cancer caused by non-ionizing ultraviolet radiation. Clear evidence establishes ultraviolet radiation, especially non-ionizing mid-wave UVB, as the cause of most non-melanoma skin cancers, which are the most common form of cancer in the world.
Ionizing radiation
Ionizing radiation sources include medical imaging, and radon gas. Ionizing radiation is not a very strong mutagen. The medical use of ionizing radiation is the source of the development of radiation-induced cancer. Ionizing radiation can be used to treat other cancers, but this can, in some cases, lead to a second form of cancer. Radiation can cause cancer in most parts of the body, in all animals, and at any age, although radiation-induced solid tumors typically take 10-15 years, and can last up to 40 years, become clinically manifest, and radiation-induced leukemia usually takes 2-10 years to appear. Radiation-induced meningiomas are a rare complication of cranial irradiation. Some people, such as those with nevoid basal cell syndrome or retinoblastoma basal syndrome, are more susceptible than the average to develop cancer from radiation exposure. Children and adolescents are twice as likely to develop leukemia from radiation as adults; radiation exposure before birth has ten times the effect.
Ionizing radiation is also used in several types of medical imaging. In industrialized countries, medical imaging accounts for nearly as much radiation dose to the public as natural background radiation. The technique of nuclear medicine involves injecting radioactive drugs directly into the bloodstream. Radiotherapy deliberately delivers high doses of radiation to the tumor and surrounding tissue as a form of disease treatment. It is estimated that 0.4% of cancers in 2007 in the United States were caused by CT done in the past and that this may increase to as high as 1.5-2% with the rate of CT use over the same time period.
Residential exposure to radon gas has the same cancer risk as passive smokers. Low-dose exposures, such as living near nuclear power plants, are generally believed to have little or no effect on cancer progression. Radiation is a potential source of cancer when combined with other cancer-causing agents, such as exposure to radon gas plus tobacco smoking.
Rare causes
Organ transplants
The development of tumors derived from donors from organ transplants is very rare. The main cause of tumor-related organ transplants appears to be malignant melanoma, which is undetectable at the time of organ harvesting. There are also reports of Kaposi's sarcoma occurring after transplantation due to tumor progression from donor cells infected with the virus.
Trauma
Physical trauma that causes cancer is relatively rare. Claims that fractures result in bone cancer, for example, have never been proven. Similarly, physical trauma is not accepted as a cause of cervical cancer, breast cancer, or brain cancer. One accepted source is the frequent long-term application of hot objects to the body. It is possible that repeated burns on the same part of the body, such as those produced by kanger and cairo heating, can produce skin cancer, especially if carcinogenic chemicals are present. Often drinking boiling hot tea can lead to esophageal cancer. Generally, it is believed that cancer appears, or pre-existing cancer is encouraged, during the process of trauma repair, rather than cancer caused directly by trauma. However, repeated injuries to the same tissue can increase excessive cell proliferation, which can then increase the likelihood of cancer mutations.
Transmission of mother-fetus
In the United States, about 3,500 pregnant women have malignancies every year, and transplacental transplacental acute leukemia, lymphoma, melanoma and carcinoma from mother to fetus have been observed. Except for the rare transmission that occurs with pregnancy and only some marginal organ donors, cancer is generally not a contagious disease. The main reason for this is the graft network rejection caused by MHC incompatibility. In humans and other vertebrates, the immune system uses MHC antigens to differentiate "self" and "non-self" cells because the antigen differs from person to person. When a non-self antigen is encountered, the immune system reacts to the corresponding cell. Such reactions can protect tumor engraftment cells by removing implanted cells.
References
Source of the article : Wikipedia
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