What Causes Cancer ?

Causes of Cancer

Cancer develops over several years and has many causes. Several factors both inside and outside the body contribute to the development of cancer. In this context, scientists refer to everything outside the body that interacts with humans as the “environment.”

Factors Outside the Body (Environmental Factors)

Exposure to a wide variety of natural and man-made substances in the environment accounts for at least two-thirds of all the cases of cancer in the United States. These environmental factors include lifestyle choices like cigarette smoking,excessive alcohol consumption,poor diet,lack of exercise, excessive sunlight exposure,and sexual behavior that increases exposure to certain viruses.Other factors include exposure to certain medical drugs, hormones, radiation, viruses, bacteria, and environmental chemicals that may be present in the air, water, food, and workplace. The cancer risks associated with many environmental chemicals have been identified through studies of occupational groups that have higher exposures to these chemicals than the general population. The importance of the environment can be seen in the differences in cancer rates throughout the world and the change in cancer rates when groups of people move from one country to another. For example, when Asians, who have low rates of prostate and breast cancer and high rates of stomach cancer in their native countries, immigrate to the United States, their prostate and breast cancer rates rise over time until they are nearly equal to or greater than the higher levels of these cancers in the United States. Likewise, their rates of stomach cancer fall, becoming nearly equal to the lower U.S. rates. Lifestyle factors such as diet, exercise, and being overweight are thought to play a major role in the trends for breast and prostate cancers, and infection with the Helicobacter pylori bacterium is an important risk factor for stomach cancer. Recently, the rapid rise in the rates of colorectal cancer in Japan and China suggests an environmental cause such as lifestyle factors. Different environmental exposures are linked to specific kinds of cancer. For example, exposure to asbestos is linked primarily to lung cancer, whereas exposure to benzidine, a chemical found in certain dyes (see page 17), is associated with bladder cancer. In contrast, smoking is linked to cancers of the lung, bladder, mouth, colon, kidney, throat, voice box, esophagus, lip, stomach, cervix, liver, and pancreas.

Factors Inside the Body

Certain factors inside the body make some people more likely to develop cancer than others. For instance, some people either inherit or acquire the following conditions: altered genes in the body’s cells, abnormal hormone levels in the bloodstream, or a weakened immune system. Each of these factors may make an individual more susceptible to cancer. One of the ways scientists know that genes play an important role in the development of cancer is from studying certain rare families where family members over several generations develop similar cancers. It appears that these families are passing on an altered gene that carries with it a high chance of getting cancer. Several genes that greatly increase a person’s chance of developing certain cancers (e.g., colon, breast, and ovary) have been identified. Only a very small percentage of people in the general population have abnormal copies of these genes. Cancers caused by these genes, known as familial cancers, account for only two to five percent of all cancers. Gene alterations may also contribute to individual differences in susceptibility to environmental carcinogens (cancer-causing substances). For instance, people differ in their ability to eliminate cancer-causing agents from their body to which they have been exposed, or to repair DNA damage that was caused by such agents. These gene alterations may also be passed on in families and account for higher rates of cancer in these families. Higher rates of cancer in families may also be related to shared environmental exposures like diet or exposure to carcinogens at work One of the main objectives of a growing field in cancer research called molecular epidemiology is to identify gene alterations that increase or decrease a person’s chance of developing cancer after an environmental exposure. Interaction of Environmental Factors and Genes Environmental factors such as viruses, sunlight, and chemicals interact with cells throughout our lives. Mechanisms to repair damage to our genes and healthy lifestyle choices (wearing protective clothing for sun exposure or not smoking) help to protect us from harmful exposures. However, over time, substances in the environment may cause gene alterations, which accumulate inside our cells. While many alterations have no effect on a person’s health, permanent changes in certain genes can lead to cancer. The chance that an individual will develop cancer in response to a particular environmental agent depends on several interacting factors—how long and how often a person is exposed to a particular substance, his/her exposure to other agents, genetic factors, diet, lifestyle, health, age, and gender. For example, diet, alcohol consumption, and certain medications can affect the levels of chemicals in the body that break down cancer-causing substances. Because of the complex interplay of many factors, it is not possible to predict whether a specific environmental exposure will cause a particular person to develop cancer. We know that certain genetic and environmental factors increase the risk of developing cancer, but we rarely know exactly which combination of factors is responsible for a person’s specific cancer. This also means that we usually don’t know why one person gets cancer and another does not.

Asbestos Lung Cancer

Asbestos is the name given to a fibrous mineral present in ore-bearing rock mined from an open pit or an underground mine. Asbestos is a group of naturally occurring fibrous minerals. The fibres can be breathed in to the lungs where they stay for plenty of years. These minerals, present in soil and rocks in plenty of parts of the world, are made of magnesium, silicon, and other elements. Some asbestos fibers are curly (or "serpentine"). The most common asbestos in industrial use, known as chrysotile, or white asbestos, has curly fibers. Other asbestos fibers are straight and needle-like (or "amphibole"). These include amosite, crocidolite, tremolite, actinolite, and anthophyllite. Asbestos fibers are resistant to heat and plenty of chemicals. As a result, asbestos has been used as an insulating material since ancient times. Since the industrial revolution, asbestos was used to insulate factories, schools, homes, and ships, to make automobile brake and clutch parts, roofing shingles, ceiling and floor tiles, cement, and textiles, and hundreds of other products. Asbestos was a common building material, but now they know that long term exposure to this mineral may cause illnesses like cancer. These substances form fibers with varying shapes and sizes and are found throughout the earth. There are three often obtainable types of asbestos; chrysotile (white asbestos), amosite (brown asbestos), and crocidolite (blue asbestos). All three have been associated with cancerous and non-cancerous lung illness.

The most common way for asbestos fibers to enter the body is through breathing. In fact, asbestos containing material isn't usually thought about to be harmful unless it is releasing dust or fibers in to the air where they can be inhaled or ingested. Lots of of the fibers will become trapped in the mucous membranes of the nose & throat where they can then be removed, but some may pass deep in to the lungs, or, if swallowed, in to the digestive tract. One time they are trapped in the body, the fibers may cause health issues. The most serious hazard of exposure to asbestos is cancer, & it takes less exposure to asbestos to cause cancer than to cause asbestosis. Three kinds of cancer are  strongly related to asbestos: lung cancer & mesothelioma. In addition, asbestos also causes cancer of the throat, stomach, esophagus, & bowel. Lung cancer caused by asbestos exposure is the same kind of cancer as that caused by smoking. It is hard to diagnose early, it spreads quickly, & can seldom be cured.

Exposure to asbestos is unlikely to cause any short term (acute) effects beyond irritation of the nose or throat. It is the long-term (chronic) effects that are debilitating & deadly. Every kind of asbestos causes cancer, & every kind of asbestos may cause asbestosis. People are exposed to asbestos chiefly through inhalation of fibers in the air they breathe. This may occur in the course of mining & processing of asbestos, in the course of the production of asbestos-containing products, or in the course of the installation of asbestos insulation. It may also occur when older asbestos-containing materials start to break down. In any of these situations, asbestos fibers tend to generate a dust composed of small particles that can float in the air. In addition, asbestos can enter the body through ingestion. This may occur when people consume contaminated food or liquids (such as water that flows through asbestos cement pipes). It may also occur when people cough up asbestos they have inhaled, then swallow their saliva. Lots of people are exposed to  low levels of naturally occurring asbestos in outdoor air due to erosion of asbestos-bearing rocks. Relatives members of asbestos workers are also potentially exposed to higher levels of asbestos because the fibers are carried home on the workers' clothing, & can then be inhaled by others in the household. Inhalation of asbestos fibers has been proven to cause lung cancer.

Lung cancer in asbestos-exposed & unexposed individuals is similar in both the type of cancer & its signs & signs. The link between cigarette smoking, asbestos & cancer of the lung itself does not apply to cancer of the lining of the lung (see malignant mesothelioma section below). Diagnosis & treatment of lung cancer is a complex topic & a pulmonary specialist ought to be involved in the workup of a suspected lung cancer. Exposure to asbestos fibers, either at home or in the workplace, is also thought about a risk factor for lung cancer. Studies show that compared to the general population, asbestos workers are three times more likely to die from lung cancer. Asbestos workers who smoke increase their risk of getting lung cancer by 50-100 times. The risk of asbestos-related abnormalities & sickness usually increases with increasing levels of exposure. This dose-response relationship is less clear for mesothelioma, where even short-term occupational exposures or secondary household exposures (e.g., household contacts of asbestos workers) have been associated with the occurrence of this malignancy. As asbestos exposures have declined in the workplace due to regulatory control, cases of extreme interstitial sickness have also decreased. Mesothelioma is a speedy spreading cancer that is  always caused by exposure to asbestos. It can take 30 or 40 years after exposure to create. Mesothelioma usually starts in the membrane that wraps around the lungs, called the pleura. The cancer cells cause a build-up of fluid between the pleura & the lungs, which in turn causes pressure on the lungs. The signs are shortness of breath & a dry, painful cough. The cancer may finally grow in to the chest wall. Often times, the cancer can create in the lining of the abdomen, the membranes of the heart or reproductive organs. Among lots of recently screened cohorts, pleural changes are more prevalent than interstitial changes. There is small proof that general environmental exposures are associated with significant sickness except in several regions of the world with endemic mesothelioma due to exposures from naturally-occurring deposits of asbestos.

Lung cancer causes the largest number of deaths related to asbestos exposure. The incidence of lung cancer in individuals who are directly involved in the mining, milling, manufacturing & use of asbestos & its products is much higher than in the general population. The most common signs of lung cancer are coughing & a alter in breathing. Other signs include shortness of breath, persistent chest pains, hoarseness, & anemia. The association between lung cancer & asbestos exposure is now well established. In the case of smokers who have had significant asbestos exposure, the risk of lung cancer is extraordinarily high. Lung cancer in asbestos exposed workers is thought to occur at a slightly earlier age than other lung cancers & are more common in the lower lobes.