Risk Factors for Cancer

Risk Factors Cancer

Also called: Hereditary Cancer Syndromes

Reviewed By:
Martin E. Liebling, M.D., FACP

Summary

A risk factor is anything that increases a person’s chance of developing a specific disease. Cancer is not a single disease but a group of more than 100 different diseases. With so many types of cancer affecting various parts of the body, the risk factors for developing cancer vary greatly depending on the specific type.

Risk factors for certain cancers can be related to environmental factors, genetic predispositions,  compromised immune systems or viral infections. Other cancers have no known causes.

Most cancers have more than one risk factor. These can include things such as age, race, sex, family history, diet, lifestyle factors, exposure to chemicals, radiation and socioeconomic status. While some risk factors are within a person’s control, such as lifestyle habits, other factors, including family history and genetics, cannot be controlled.

Having one or more risk factors for a type of cancer means an individual is more likely to develop that disease. It does not mean the person will absolutely develop the disease. In some cases, people with known risk factors never have cancer in their lifetime. In other cases, cancer occurs in seemingly healthy people with no risk factors. The relationship of risk factors to disease is never completely certain because after a  person develops cancer, there is no way to prove a risk factor was responsible for causing the disease. However, there are some statistical likelihoods, such as lung cancer developing in someone who smokes heavily.

About risk factors for cancer

Cancer is a group of more than 100 different diseases, each with its own unique set of risk factors. Risk factors are elements that increase the possibility of developing a specific disease or condition. Over a lifetime, it is estimated that one in three people will develop cancer, according to the National Cancer Institute (NCI).

Cancer develops as a result of an uncontrolled growth of cells. In normal cell function, cells divide and die in an organized fashion. As cells grow old, they die, allowing for new cells to take their place. When old cells do not die and the body continues to create new cells, they collect to form a tumor A tumor can be either benign (noncancerous) or malignant (cancerous).

There is more than one risk factor for most cancers. Some risk factors can be controlled, such as lifestyle habits. These factors can include smoking, alcohol use, diet and exercise. Other risk factors cannot be controlled by an individual, such as age, race, sex and genetic factors.

Although risk factors may be divided into controllable and uncontrollable categories, such distinctions may be counterproductive. In many cases, an environmental risk factor may combine with a genetic predisposition and create an opportunity for cancer to develop. Researchers believe that the development of cancer often involves environmental factors that directly or indirectly alter cells. These experts contend that nearly all cancers occur as a result of a combination of factors and it is nearly impossible to determine a single cause. Controllable and uncontrollable factors can combine to a point where identifying one or the other as the exact cause is extremely difficult. 

The division of risk factors into categories may serve to provide better awareness for both patients and medical professionals. Awareness of controllable risk factors can help patients avoid them by quitting smoking, maintaining a healthy weight and protecting their skin from sun exposure. Awareness of both controllable and uncontrollable risk factors in a patient’s medical history provides physicians with valuable information to schedule screening tests and make diagnoses.

Many risk factors have been identified by scientists conducting epidemiological studies that analyze both environmental and genetic risk factors. According to the American Cancer Society, about 75 to 80 percent of cancers can be attributed to environmental factors, including tobacco use, diet, infectious agents and occupational exposure.

Much of this information has come from studying people who migrate from an area of high cancer risk to an area of low cancer risk (or vice versa). These migrant studies demonstrate that these people soon take on the cancer rates of their new area. Because genetic changes take several generations, it suggests that the cancer attack rates may be related to environmental causes.

Controllable risk factors for cancer

Different cancers have different risk factors. Some of the major risk factors associated with various cancers that are considered controllable include:

  • Tobacco use. A direct link between smoking and cancers of the lung, mouth, larynx, bladder, kidney, cervix, esophagus and pancreas has been established. Tobacco use includes cigarettes, cigars, pipe smoking, chewing tobacco and snuff. Smoking causes one-third of all cancer deaths and is the number one cause of preventable death in the United States, according to the National Cancer Institute (NCI). Like smoking, chewing tobacco is also considered a carcinogen (cancer-causing substance). It is strongly linked to oral, oropharyngeal and laryngeal cancers. Since snuff is placed directly against mouth tissues, it greatly increases the risk of oral cancers. In addition, nonsmokers who spend significant time around smokers are exposed to secondhand smoke, which increases their risk for lung cancer.

  • Obesity, diet and exercise. The body’s immune system is significantly helped by the maintenance of an ideal weight through proper nutrition and regular exercise. Obesity is a known risk factor for several cancers, including cancer of the breast, colon, rectum, kidney, uterus and gallbladder. Some recent research also links obesity to an increased risk of ovarian cancer. It is estimated that nearly one-third of all cancer deaths are related to a combination of dietary factors and lack of physical activity in adulthood. For example, a high-fat diet may play a role in prostate cancer and colorectal cancer. The body’s immune system is bolstered through moderate exercise and proper nutrition.
  • Alcohol and drugs. The excessive use of alcohol and addictive drugs can weaken the body’s defense system. When the immune system is weakened, the body is less able to fight off disease, including cancer. For example, some studies have shown a connection between alcohol consumption and an increased risk of breast cancer. Alcohol is also a risk factor for cancers in other body areas, including the lungs, mouth, lips, colon, pancreas, liver, esophagus and the larynx.

  • Ultraviolet (UV) radiation. Each year, more than 1 million skin cancers are diagnosed in the United States, according to the American Cancer Society (ACS). Non-melanoma skin cancer is the leading type of cancer diagnosed in the United States. Many of these cases could have been prevented through proper protection from the sun’s ultraviolet rays.

  • Occupational exposure. According to the U.S. Centers for Disease Control and Prevention (CDC), each year an estimated 20,000 cancer deaths and 40,000 new cancer diagnoses are related to occupational exposure. Professions that are considered high-risk include uranium miners, and workers in asbestos factories, nuclear power plants and chemical plants.

    Certain chemicals, metals and pesticides can increase the risk of cancer. Some of the more commonly recognized carcinogens that workers can be exposed to include asbestos, nickel, formaldehyde, cadmium, uranium, vinyl chloride, benzidine and benzene. Occupational exposures to substances such as solvents, pesticides, oil products, rubber, vinyl chloride, or ionizing radiation may increase the risk of developing cancer. Working with tobacco products also appear to increase the risk of certain cancers. In most cases, the risk of developing cancer increases with the level and length of exposure.
  • High risk carcinogenic chemicals include:

    Carcinogen Industry Type of cancer Arsenic Mining, pesticides Lung cancer, skin cancer, liver cancer Asbestos Construction Lung cancer, mesothelioma Benzene Petroleum, rubber, chemical Leukemia Chromium Metal, electroplating Lung cancer Leather dust Shoe manufacturing Bladder cancer, nasal cavity and paranasal sinus cancer Naphthylamine Chemical, dye, rubber Bladder cancer Radon Underground mining Lung cancer Soots, tars, oils Coal, gas, petroleum Lung cancer, skin cancer, liver cancer Vinyl chloride Rubber, polyvinyl chloride manufacturing Liver cancer Wood dust Furniture manufacturing Nasal cavity and paranasal sinus cancer
  • Radon. This radioactive gas is present in nearly all air as a result of being released from decaying uranium that is in rocks and soil. Radon levels vary, but can enter homes through tiny cracks in the walls, floors or foundations, as well as being released from building materials. This can be a significant problem for homes that are well-insulated or built over soil that has high levels of uranium. People who are exposed to radon over long periods of time can develop lung cancer. These lung cancer cases have occurred in both smokers and nonsmokers. Both the National Toxicology Program and the International Agency for Research on Cancer have classified radon as a known human carcinogen. Testing the indoor air quality is the only way to detect radon in the home.

  • Pollution. The exhaust from vehicles and the air pollution from industrial power plants increase the risk of lung cancer in people exposed over a long period of time, according to the ACS.

  • Heterocyclic amines (HCAs). Research from the NCI has shown that certain muscle meats (beef, pork, fowl and fish) cooked at high temperatures, particularly on a grill, create chemicals that increase cancer risk. Among these chemicals, heterocyclic amines (HCAs) may pose a human cancer risk.

  • Radiation exposure. Diagnostic tests, including x-rays and computerized axial tomography (CAT) scan are being used more often among the general population due to increased availability. However, there is a link between radiation exposure and the development of cancer in a person’s lifetime. This is of particular concern for children because the NCI estimates that between 2 million and 3 million CAT scans are performed on children each year. The benefits of such tests may outweigh the risks and newer techniques and equipment have decreased the amount of radiation exposure. Radiation exposure during cancer treatment may also increase the risk of developing another cancer.

  • Reproductive and hormonal factors. This category mainly pertains to women and has received considerable attention over the years. Many hormonal and reproductive factors have been associated with either risk or prevention of cancers. For example, if a woman has children before the age of 30 her risk of breast cancer decreases. The risk of cervical cancer increases in women who have a history of sexually transmitted diseases. Other related risk factors include:

    • Not breastfeeding. Breastfeeding seems to have a protective effect on both mother and child. For mothers who breastfed their children, a lower incidence of breast cancer has been reported, while those who did not breast feed had a higher rate of breast cancer.

    • Diethylstilbestrol (DES). This synthetic form of estrogen was used by pregnant women between the early 1940s and 1971. Its use increased the risk of women developing breast cancer and cervical cancer. The daughters born from DES-exposed pregnancies have shown increased risks of some rare cervical and vaginal cancers, in addition to fertility problems and pregnancy complications.

    • Fertility drugs. Research studies have reached conflicting results on whether or not fertility drugs increase a woman’s risk of developing ovarian cancer or uterine cancer.

    • Oral contraceptives. Birth control pills have been linked to an increased risk of cancer, particularly breast cancer. 

    • Hormone replacement therapy (HRT). HRT or other extended exposure to estrogen or progesterone increases a woman’s risk of developing breast cancer. The risk varies based on a number of factors such as menopausal status and reproductive history. A considerable amount of research has been devoted to the benefits and risks of HRT in women.

In addition to individual risk factors, certain lifestyle choices or behaviors can dramatically increase a person’s risk for cancer, particularly when they are combined. These factors which include tobacco use, alcohol use, diet, infectious diseases, as well as exposure to chemicals and radiation, cause an estimated 75 percent of all cancer cases in the United States. Tobacco use, unhealthy diet and physical inactivity are considered the most likely factors to affect personal cancer risk.

Uncontrollable risk factors for cancer

In addition to the many controllable risk factors, there are a number of factors that increase a person’s risk for developing cancer that are outside a person’s control. These include:

  • Age. The risk of many cancers, such as breast, prostate,colorectal and others increase with age.
  • Ethnicity. Certain cancers are more prevalent in specific populations. For example, although it is not known why, prostate cancer is more common among African American men than among white men. Women from an Ashkenazi (Eastern European) Jewish background are more likely to have a genetic mutation that increases their risk for breast cancer.

  • Family history of cancer. Some cancers are said to “run in families.” Ovarian cancer and breast cancer are two common examples. Women with a mother or sister who has had either disease are more likely to develop the disease themselves.

  • Genetic conditions. Hereditary cancer syndrome is a term used when several members of a family have cancer because of an inherited abnormal (mutated) gene. Increased risk of cancer is associated with hundreds of hereditary conditions, according to the National Cancer Institute (NCI), including von Hippel-Lindau disease, Li-Fraumeni syndrome, Turcot syndrome or neurofibromatosis. The more prominent cancers that may have a genetic link include breast cancer, prostate cancer, colorectal cancer and melanoma.

    Conditions that may increase cancer risk include:

    Condition Type of cancer Hereditary retinoblastoma Retinoblastoma Xeroderma pigmentosum Skin cancer Wilms’ tumor Kidney cancer Li-Fraumeni syndrome Sarcomas, brain cancer, breast cancer, leukemia Familial adenomatous polyposis Colorectal cancer Paget’s disease of bone Bone cancer Fanconi’s aplastic anemia Leukemia, liver cancer, skin cancer
  • In some cases, tests are available to detect whether a person carries certain genetic mutations that can increase the risk for cancer. Women may be tested for mutations to certain genes, including BRCA1 and BRCA2, which may indicate an increase risk for breast cancer. For patients with a family history of a certain type of cancer, taking such a test may provide more information about their risks. However, these tests have advantages and disadvantages and their use should be discussed with appropriate physicians.

  • Gender. While many cancers show equal prevalence among gender lines, some are exclusively male or female, while some favor a particular gender. For example, all men are at risk for prostate cancer while all women (but many fewer men) are at risk for breast cancer.
  • Previous history of cancer. After a person has had cancer, the risk of recurrence, depending on the type of cancer can be considerable for the first two to three years following diagnosis and treatment. It is also possible to be predisposed for other cancers after being diagnosed with a first cancer. It may be the actual cancer or treatment for the cancer that increases a person’s risk of a second cancer.
  • Radiation or chemotherapy. According to the NCI, children who received chemotherapy or radiation therapy for cancer are at risk for developing a second primary cancer. Accidental exposure to high doses of ionizing radiation has also been linked to increased risk of childhood cancers. Additionally, certain chemotherapy drugs may lead to an increased risk of leukemia.

  • Infectious exposure. Some forms of cancer may be related to exposure to viral or bacterial infections and could be prevented by lifestyle changes or vaccines. The bacterium Helicobacter pylori occurs in the stomach and is responsible for many peptic ulcers and is closely associated with stomach cancer. H. pylori infection can be treated with antibiotics. It is more common in developing countries, where people may have more limited access to antibiotics. These areas have corresponding higher rates of stomach cancer.

    The Epstein-Barr virus, which causes mononucleosis, has a close association with lymphoma and other cancers. Human papillomaviruses (HPVs) are not a single virus, but rather are a group of more than 100 types of viruses. Certain HPVs  have a close association with the development of cervical cancer and anal cancer. In 2006, a vaccine was introduced to protect against the strains of HPV most closely associated with cervical cancer. Studies have also shown a link between children and adults with AIDS and an increased risk of non-Hodgkin’s lymphoma, leiomyosarcoma (a type of muscle cancer) and Kaposi’s sarcoma, among other cancers. Only a small number of viruses are considered a cause of cancer, including:

    Virus Type of cancer Epstein-Barr virus Burkitt’s lymphoma Hepatitis B and C virus Liver cancer Human papillomavirus Cervical cancer Human T-cell lymphotrophic virus Adult T-cell leukemia Kaposi’s sarcoma-associated herpesvirus Kaposi’s sarcoma

Potential (unproven) factors

Controllable and uncontrollable factors often coincide to a point where it is impossible to determine the exact cause of a cancer. There are other factors that are often considered potential causes but have not been scientifically proven. Among the most common are:

  • Electromagnetic fields. Some people believe that living near power lines and electromagnetic fields can increase the risk of cancer, especially in children. Studies thus far have reached inconclusive and oftentimes inconsistent results. In addition, cordless and cellular telephones have been under scrutiny as a possible cause for cancer, particularly brain cancers. However, because this technology has not been in use for an extended length of time, there has not been ample opportunity to conduct long-term studies. Current studies have not proven a definitive association between cell phone use and brain tumors.
  • Psychological stress. There is a complex relationship between physical and psychological health and it is not completely understood. Scientists acknowledge that stress can activate the body’s endocrine (hormone) system, which can lead to immune system changes. Immune system changes make the body less able to fight infection and diseases. Still, a direct link has yet to be established between stress and cancer. While studies have shown that stress factors alter the immune system, no direct cause-and-effect relationship has been established.
  • Toxic waste. The toxic chemicals and substances in dump sites and waste areas have been studied for causal relationship to cancer. Although many of the substances can be hazardous to people’s health, studies have not proven their exact role in causing cancers.

There is a considerable amount of research being devoted to the relationship between elements found in people’s daily lives and cancer. Scientists continue to examine many areas in an attempt to discover possible contributions and causes of the disease.

Questions for your doctor about risk factors

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about cancer risk factors:

  1. Which cancers present the greatest risk for me based on my family history?
  2. What changes in lifestyle can I make to reduce my risk of cancer?
  3. Am I using any medications that will increase my risk of cancer?
  4. Is there a way to eliminate these medications to lower my risk?
  5. How does my reproductive history affect my chances of developing cancer?
  6. Are there any tests that might indicate my risk for cancer?
  7. Can any complementary or alternative medicines help reduce my risk?
  8. Do you recommend any genetic testing for me or members of my family?
  9. Will exposure to chemicals in my past affect my cancer risk?
  10. Will I pass on my increased risks to my children?
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