Lung Cancer Risk Factors

A risk factor is anything that increases a person's chance of getting a disease such as cancer. Different cancers have different risk factors. For example, exposure to sunlight is a risk factor for skin cancer and a high-fat, low-fiber diet is a risk factor for colorectal cancer. The number one risk for lung cancer is tobacco smoking.

Risk Factors for Lung Cancer

Tobacco Smoking

By far the most prominent risk factor is tobacco smoking. More than 80% of lung cancers are thought to result from smoking. The longer a person has been smoking and the more packs per day smoked, the greater the risk. If a person stops smoking before a cancer develops, the damaged lung tissue starts to gradually return to normal. Even after ten years, the ex-smoker's risk still does not equal the lower risk of a person who never smoked. However, an ex-smoker's risk is about half the risk of people who continue to smoke.

Nonsmokers who breathe in the smoke of others (also called second hand smoke or environmental tobacco smoke) are also at increased risk for lung cancer. A nonsmoker who is married to a smoker has a 30% greater risk of developing lung cancer than the spouse of a nonsmoker.

Asbestos

Death from lung cancer is about seven times more likely to occur among asbestos workers than among the general population. Exposure to asbestos fibers is an important risk factor for lung cancer. Asbestos workers who smoke have a very high lung cancer risk: 50 to 90 times greater than that of people in general. Both smokers and nonsmokers exposed to asbestos also have a greater risk of developing a type of cancer which starts from the pleura (the layer of cells that line the outer surface of the lung). This cancer is called mesothelioma.

In recent years, the government has nearly stopped the use of asbestos in commercial and industrial products. Because asbestos was used for so many years, it is a good idea to check and see if there might be asbestos in products or in houses before buying them.

Radon

Radon is a radioactive gas produced by the natural breakdown of uranium that cannot be seen, tasted or smelled. Outdoors, there is so little radon that it is not a danger. But indoors, radon can be more concentrated and can become a possible risk for cancer. Recently, concerns have been raised about houses in some parts of the United States built over soil with natural uranium deposits that can create high indoor radon levels. State and local offices of the Environmental Protection Agency can provide the names of reliable companies that perform radon testing and renovation. High radon levels in some mines can increase the lung cancer risk for miners.

Cancer-causing Agents in the Workplace

In addition to asbestos and radon, there are other cancer-causing agents (carcinogens) in the workplace. People at risk include miners who may breathe in radioactive ores such as uranium and workers exposed to chemicals such as arsenic, vinyl chloride, nickel chromates, coal products, mustard gas and chloromethyl ethers. The government and industry have taken major steps in recent years to protect workers. But the dangers are still present, and those who work in these conditions should be very careful to avoid exposure.

Marijuana

Marijuana cigarettes contain more tar than tobacco cigarettes. Also, they are inhaled very deeply and the smoke is held in the lungs for a long time. Marijuana cigarettes are also smoked all the way to the end where tar content is the highest. Many of the cancer-causing substances in tobacco are also found in marijuana. Because marijuana is an illegal substance, it is not possible to control whether it contains fungi, pesticides and other additives. Medical reports suggest marijuana may cause cancers of the mouth and throat.

The connection between marijuana and lung cancer has been hard to prove because it is not easy to gather information about the use of illegal drugs. Also, many marijuana smokers also smoke tobacco cigarettes. This makes it difficult to know how much of the risk is from tobacco and how much is from marijuana.

Recurring Inflammation

Tuberculosis and some types of pneumonia often leave scarred areas on the lung. This scarring increases the risk of the person developing the adenocarcinoma type of lung cancer.

Talcum Powder

While no increased risk of lung cancer has been found from the use of cosmetic talcum powder, some studies of talc miners and millers suggest a higher risk of lung cancer and other respiratory diseases from their exposure to industrial grade talc. Talcum powder is made from talc, a mineral that in its natural form may contain asbestos. By law since 1973, all home-use talcum products (baby, body, and facial powders) have been asbestos-free.

Other Mineral Exposures

People with silicosis and berylliosis (lung diseases caused by breathing in certain minerals) also have an increased risk of lung cancer.

Personal and Family History

People who have lung cancer have an increased risk of another lung cancer. Brothers, sisters and children of those who have had lung cancer may have a slightly higher risk of lung cancer themselves. However, it is difficult to say how much of this excess risk is due to inherited factors and how much is due to environmental tobacco smoke.

Vitamin A Deficiency or Excess

People who do not get enough vitamin A are at increased risk of lung cancer. On the other hand, taking too much vitamin A may also increase lung cancer risk.

Air Pollution

In some cities, air pollution may slightly increase the risk of lung cancer. This risk is far less than that caused by smoking.

Can Lung Cancer be Prevented?

The best way to prevent lung cancer is to not smoke. People should not start smoking, and those who already smoke should quit. Everyone should avoid breathing in other people's smoke. People should find out about cancer-causing chemicals they may be exposed to at work and take appropriate protective measures. Persons who live in areas where national uranium deposits in the soil release radon gas should consider testing radon levels in their homes.

Nevertheless, in some people who get lung cancer risk factors are not apparent. At this time, it is not possible to give advice on how to prevent all cases of lung cancer.

Do we know what causes lung cancer?

Tobacco smoking is by far the leading cause of lung cancer. Over 80% of lung cancers are caused by smoking.

Other risk factors for lung cancer include a family or personal history of lung cancer and exposure to cancer-causing agents in the workplace or the environment.

During the past few years, scientists have made great progress in understanding how certain changes in DNA can cause normal lung cells to grow abnormally and form cancers. DNA is the genetic material that carries the instructions for nearly everything our cells do. We usually resemble our parents because they passed their DNA on to us. However, DNA affects more than our outward appearance. Some genes (parts of our DNA) contain instructions for controlling when cells grow and divide. Certain genes that promote cell division are called oncogenes. Others that slow down cell division or cause cells to die at the appropriate time are called tumor suppressor genes. It is known that cancers can be caused by DNA mutations (defects) that activate (turn on) oncogenes or inactivate (turn off) tumor suppressor genes. Some people inherit DNA mutations from their parents that greatly increase their risk for developing breast, ovarian, colorectal and several other cancers. However inherited oncogene or tumor suppressor gene mutations are not felt to be a cause of very many lung cancers.

Oncogene and tumor suppressor gene mutations related to lung cancer usually develop during life rather than before birth as an inherited mutation. Every time a cell prepares to divide into two new cells, it must duplicate its DNA. This process is not perfect and sometimes, copying errors occur. Fortunately, cells have repair enzymes that proofread DNA. But some errors may slip past, especially if the cells are growing rapidly. Acquired mutations in lung cells often result from exposure to cancer-causing chemicals in tobacco smoke. Acquired changes in genes, such as the p53 tumor suppressor gene and the ras oncogene, are thought to be important in the development of lung cancer. Changes of these and similar genes may also be responsible for making some lung cancers likely to grow and invade more rapidly than others. Current research in this field is aimed at developing tests that can detect lung cancers at an early stage by recognizing their DNA changes. Other researchers are working on gene therapy strategies for repairing or replacing these mutated genes in order to stop the abnormal growth and spread of the cancer cells.

Although lung cancers only rarely result from inherited mutations of oncogenes or tumor suppressor genes, some people seem to inherit a reduced ability to detoxify (break down) certain types of cancer-causing chemicals. These people are more sensitive to the cancer-causing effects of tobacco smoke and certain industrial chemicals. Researchers are developing tests that may help identify such people, but these tests are not yet reliable enough for routine use. Therefore, doctors recommend that all people avoid tobacco smoke and hazardous industrial chemicals.