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Jai Ganesh

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Carcinogen

Carcinogen

Gist

A carcinogen is a substance, organism or agent capable of causing cancer. Carcinogens may occur naturally in the environment (such as ultraviolet rays in sunlight and certain viruses) or may be generated by humans (such as automobile exhaust fumes and cigarette smoke).

Summary

Carcinogen is any of a number of agents that can cause cancer in humans. They can be divided into three major categories: chemical carcinogens (including those from biological sources), physical carcinogens, and oncogenic (cancer-causing) viruses.

Most carcinogens, singly or in combination, produce cancer by interacting with DNA in cells and thereby interfering with normal cellular function. This ultimately results in the formation of a tumour (an abnormal tissue growth) that has the ability to spread (metastasize) from its site of origin and invade and cause dysfunction of other tissues, culminating in organ failure and death. The two primary mechanisms by which carcinogens initiate the formation of such tumours is via alterations in DNA that encourage cell division and that prevent cells from being able to self-destruct when stimulated by normal triggers, such as DNA damage or cellular injury (a process known as apoptosis). There also exist carcinogens that induce cancer through nongenotoxic mechanisms, such as immunosuppression and induction of tissue-specific inflammation.

More than 400 chemical agents have been listed as carcinogenic, probably carcinogenic, or possibly carcinogenic by the International Agency for Research on Cancer (IARC), a branch of the World Health Organization that monitors cancer occurrence worldwide and performs epidemiological and laboratory investigations to understand the causes of cancer. Among the carcinogenic substances listed by IARC are a variety of chemical effluents from industry and environmental pollutants from automobiles, residences, and factories. One such example is acrylamide, which is considered a probable carcinogen in humans and is produced as a result of industrial processes and cooking certain foods at high temperatures. It can be released into the environment through its application in wastewater treatment and its use in grout and soil-stabilizer products. Other examples of chemical carcinogens include nitrosamines and polycyclic aromatic hydrocarbons, which are found in tobacco smoke and are associated with the development of lung cancer.

Physical carcinogens include ultraviolet rays from sunlight and ionizing radiation from X-rays and from radioactive materials in industry and in the general environment. Repeated local injury (e.g., wounding) or recurring irritation (e.g., chronic inflammation) to a part of the body are other examples of potential physical carcinogens.

A number of viruses are suspected of causing cancer in animals, including humans, and are frequently referred to as oncogenic viruses. Examples include human papillomaviruses, the Epstein-Barr virus, and the hepatitis B virus, all of which have genomes made up of DNA. Human T-cell leukemia virus type I (HTLV-I), which is a retrovirus (a type of RNA virus), is linked to tumour formation in humans.

Some—not all—cancers are heritable in the sense that a predisposition exists, awaiting a convergence of carcinogenic influences for cancer to manifest itself. The identification and timely elimination of carcinogens can reduce the incidence of cancer.

Details

A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive substances are considered carcinogens, but their carcinogenic activity is attributed to the radiation, for example gamma rays and alpha particles, which they emit. Common examples of non-radioactive carcinogens are inhaled asbestos, certain dioxins, and tobacco smoke. Although the public generally associates carcinogenicity with synthetic chemicals, it is equally likely to arise from both natural and synthetic substances. Carcinogens are not necessarily immediately toxic; thus, their effect can be insidious.

Carcinogens are agents in the environment capable of contributing to cancer growth. Carcinogens can be categorized into two different types: activation-dependent and activation-independent, and each nature impacts their level and type of influence when it comes to promoting cancer growth. Activation-dependent carcinogens require metabolic activation or modification to induce cancer, while activation-independents ones do not. Examples of activation-dependent carcinogens range from certain viruses, such as HPV, to consumed alcohol, to excessive amounts of red and processed meats, impacting a person's health in ways they may not immediately associate with cancer. Activation-independent carcinogens, such as ultraviolet rays or nitrosamines in tobacco products, possess characteristics enabling them to interact directly with DNA and other cellular components to cause harm. These include not requiring metabolic action or molecular changes to act, which complements their ability to be electrically excited, permitting them to interact with oxygen and nitrogen atoms in negatively charged cellular environments. This type of interaction leads to the alteration of DNA nucleotide bases, causing disarrangement of that genetic material. This disarrangement is also responsible for the formation of DNA adducts, segments of DNA which bind to carcinogens, which furthers harm. Eventually, failure in DNA repair mechanisms will lead to a buildup of DNA damage and potentially the development of cancer.

There are many natural carcinogens. Aflatoxin B1, which is produced by the fungus Aspergillus flavus growing on stored grains, nuts and peanut butter, is an example of a potent, naturally occurring microbial carcinogen. Certain viruses such as hepatitis B and human papilloma virus have been found to cause cancer in humans. The first one shown to cause cancer in animals is Rous sarcoma virus, discovered in 1910 by Peyton Rous. Other infectious organisms which cause cancer in humans include some bacteria (e.g. Helicobacter pylori) and helminths (e.g. Opisthorchis viverrini and Clonorchis sinensis).

Dioxins and dioxin-like compounds, benzene, kepone, EDB, and asbestos have all been classified as carcinogenic. As far back as the 1930s, industrial smoke and tobacco smoke were identified as sources of dozens of carcinogens, including benzopyrene, tobacco-specific nitrosamines such as nitrosonornicotine, and reactive aldehydes such as formaldehyde, which is also a hazard in embalming and making plastics. Vinyl chloride, from which PVC is manufactured, is a carcinogen and thus a hazard in PVC production.

Additional Information

Carcinogens are substances that may increase your risk of developing cancer. Experts have identified more than 100 carcinogens. Carcinogens may be physical, such as ultraviolet rays from the sun; chemical, like asbestos; or biological, such as infections caused by certain viruses. Simply having contact with a carcinogen doesn’t mean you’ll develop cancer. While you may not be able to avoid some carcinogens, there are steps you can take to reduce your risk of developing cancer from carcinogen exposure.

How do carcinogens cause cancer?

To understand how carcinogens cause cancer, it may help to know more about the relationship between carcinogens and your genetic makeup.

Your DNA is in your genes. Your genes contain instruction manuals for making proteins. Proteins control millions of actions, including how cells grow and multiply. When a carcinogen changes your DNA, it triggers a chain reaction that turns normal cells into cancerous cells.

Sometimes, carcinogens do direct damage to your DNA so it stops working as it should. Other times, cells that typically repair DNA damage from carcinogens can’t take care of the issue. Left unrepaired, damaged DNA may lead to changes (mutations) in certain genes.

Depending on the specific mutation or change, your genes may start giving cells instructions to multiply uncontrollably, becoming cancerous tumors or blood cancer. But cancer doesn’t develop right away. Carcinogens build up over time. It may take years before a carcinogen in your body begins the chain reaction that leads to cancer.

How would I have contact with a carcinogen?

You may have contact with a carcinogen if:

* You have certain lifestyle habits such as using tobacco.
* You spend time in a workplace that uses carcinogenic chemicals to make products.
* You have certain viruses, like human papillomavirus (HPV), that cause cancer.

Again, simply having contact with a carcinogen doesn’t mean you’ll develop cancer. Factors that increase cancer risk include:

* Longtime exposure to a carcinogen. For example, someone who uses tobacco, has used tobacco for many years or is exposed to second-hand smoke is more likely to have cancer than someone who’s never used tobacco, quit using tobacco and avoids second-hand smoke.
* Extensive exposure to a carcinogen. For example, drinking significant amounts of beverages containing alcohol increases your cancer risk. According to the American Cancer Society, men and people assigned male at birth (AMAB) should limit their intake to two drinks a day. Women and people assigned female at birth (AFAB) should limit intake to one drink a day.
* Genetic (inherited) mutations. About 5% to 12% of cancers are inherited, meaning people are born with genetic mutations that cause cancer. Someone who has an inherited cancer and is exposed to carcinogens has an increased risk of developing cancer.

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