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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Alonso Alvarado, M.D. [2]

Overview

Factors that increase the chance of developing cancer are called risk factors. There are 2 types of risk factors: Modifiable and Non-modifiable. Modifiable risk factors are attitudes or circumstances that people can avoid, for example smoking. Non-modifiable risk factors are conditions that can't be changed, for example genetic predisposition to certain diseases. Factors that decrease the chance of developing cancer are called protective factors.

Factors That are Known to Increase the Risk of Cancer

Tobacco

Information below is based on the National Cancer Institute Cancer Prevention Overview: Risk Factors page.[1]

  • Tobacco use is strongly linked to an increased risk for many kinds of cancer. Cigarette smoking is the leading cause of the following types of cancer:

Infections

Information below is based on the National Cancer Institute causes and risk factors page.[2][3][4]

Certain viral and bacterial infections are able to cause cancer. Infection as a cancer cause is more common in developing countries (about 1 in 4 cases of cancer) than in developed countries (less than 1 in 10 cases of cancer). Examples of infection caused cancers:

  • Human immunodeficiency virus (HIV): People infected with HIV have a substantially higher risk of some types of cancer compared with uninfected people of the same age.
  • Human papillomavirus (HPV): HPV infections are the most common sexually transmitted infections in the United States. High-risk or oncogenic HPVs, which can cause cancer. At least 13 high-risk HPV types have been identified: 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, and 68. wo of these, HPV types 16 and 18, are responsible for the majority of HPV-caused cancers.
  • During a nearly 15-year period after treatment, gastric cancer incidence was reduced by almost 40%

Two vaccines to prevent infection by cancer-causing agents have already been developed and approved by the U.S. Food and Drug Administration (FDA):

Radiation

There are two main types of radiation linked with an increased risk for cancer:[1]

  • Ultraviolet radiation from sunlight: This is the main cause of nonmelanoma skin cancers.
  • Ionizing radiation including:
  • Radiation exposure from diagnostic X-rays increases the risk of cancer in patients and X-ray technicians.
  • The growing use of CT scans over the last 20 years has increased exposure to ionizing radiation. The risk of cancer also increases with the number of CT scans a patient has and the radiation dose used each time.

Ionizing radiation has been associated with:

Non-ionizing radiation:[5]

  • The most common exposures to radiofrequency energy are from telecommunications devices and equipment (cell phones, chordless phones). Other radiofrequency energy sources are: AM/FM radios and VHF/UHF televisions, radar, satellite stations, magnetic resonance imaging (MRI) devices, industrial equipment, and microwave ovens.
  • It is generally accepted that damage to DNA is necessary for cancer to develop. However, radiofrequency energy, unlike ionizing radiation, does not cause DNA damage in cells, and it has not been found to cause cancer in animals or to enhance the cancer-causing effects of known chemical carcinogens in animals.
  • The American Cancer Society, the National Institute of Environmental Health Sciences, the FDA and the CDC have concluded that there is not enough evidence to consider non-ionizing radiofrequency energy as a cause for cancer.
  • The International Agency for Research in Cancer classified radiofrequency fields as “possibly carcinogenicto humans”.

Immunosuppressive Medicines

Immunosuppressive medicines are linked to an increased risk of cancer because these medications lower the immune system's ability to stop cancer from forming.[1]

Asbestos exposure

Information below is based on the National Cancer Institute Asbestos Exposure and Cancer Risk page.[6]

  • Asbestos has been classified as a known human carcinogen by the U.S. Department of Health and Human Services, the EPA, and the International Agency for Research on Cancer.
  • Studies have shown that exposure to asbestos may increase the risk of lung cancer and mesothelioma.
  • Mesothelioma is the most common form of cancer associated with asbestos exposure.
  • Though inconclusive, studies have shown an association between asbestos and other cancers:

Formaldehyde

Information below is based on the National Cancer Institute Formaldehyde and Cancer Risk page.[7]


  • The International Agency for Research on Cancer (IARC) and the National Toxicology Program classify formaldehyde as a human carcinogen.
  • Several National Cancer Institute (NCI) surveys suggested that professionals who are potentially exposed to formaldehyde in their work, such as anatomists and embalmers, have an increased risk of leukemia (particularly myeloid leukemia) and brain cancer compared with the general population.
  • Several epidemiologic studies have shown the risk of formaldehyde exposure and cancer. This risk was associated with increasing peak, average levels and duration of exposure, but it was not associated with cumulative exposure.
  • A 10-year follow-up study showed the risk of leukemia was highest earlier in the follow-up period. Risks declined steadily over time, such that the cumulative excess risk of myeloid leukemia was no longer statistically significant at the end of the follow-up period.
  • Several case-control studies, as well as analysis of the large NCI industrial cohort, found an association between formaldehyde exposure and nasopharyngeal cancer.
  • Data from extended follow-up of the NCI cohort found that the excess of nasopharyngeal cancer observed in the earlier report persisted.

Hair dye

Information below is based on the National Cancer Institute Hair Dyes and Cancer Risk page.[8]

  • Studies have shown that professional hairdressers have an increased risk of bladder cancer that may be due to occupational exposure to hair dye. However, the information is inconclusive.
  • A review of 14 studies of female breast cancer and hair dye published between 1977 and 2002 found that dye users had no increase in the risk of breast cancer compared with nonusers.
  • Studies of the association between personal hair dye use and the risk of leukemia have had conflicting results.

Acrylamide

Information below is based on the National Cancer Institute Acrylamide in Food and Cancer Risk page.[9]

  • The National Toxicology Program and the International Agency for Research on Cancer consider acrylamide to be a “probable human carcinogen,” based on studies in laboratory animals.
  • One study showed that women with higher levels of acrylamide bound to the hemoglobin in their blood, had a statistically significant increase in risk of estrogen receptor-positive breast cancer.
  • A questionnaire-based cohort study performed the Netherlands found an excess of endometrial and ovarian cancer associated with higher levels of acrylamide exposure

Artificial sweeteners

Information below is based on the National Cancer Institute Artificial Sweeteners and Cancer Risk page.[10]

  • Studies in rats showed an increased incidence of bladder cancer at high doses of saccharin, especially in male rats. However, mechanistic studies have shown that these results apply only to rats.
  • Human epidemiology studies have shown no consistent evidence that saccharin is associated with bladder cancer incidence.
  • Aspartame: NCI examined human data from the NIH-AARP Diet and Health Study of over half a million retirees. Increasing consumption of aspartame-containing beverages was not associated with the development of lymphoma, leukemia, or brain cancer.
  • Acesulfame potassium, Sucralose and Neotame: These three artificial sweeteners are currently permitted for use in food in the United States. Before approving these sweeteners, the FDA reviewed more than 100 safety studies that were conducted on each sweetener, including studies to assess cancer risk. The results of these studies showed no evidence that these sweeteners cause cancer or pose any other threat to human health.
  • Cyclamate: Early studies showed that cyclamate in combination with saccharin caused bladder cancer in laboratory animals.
  • Results from subsequent studies of cyclamate’s carcinogenicity and the evaluation of additional data, it was concluded that cyclamate was not a carcinogen or a co-carcinogen.
  • A food additive petition was filed with the FDA for the reapproval of cyclamate, but this petition is currently being held in abeyance. The FDA’s concerns about cyclamate are not cancer related.

Genetics

Information below is based on the National Cancer Institute Genetic Testing for Hereditary Cancer Syndromes page.[11]

Genetic mutations play a role in the development of all cancers. Most of these mutations occur during a person’s lifetime, but some mutations, including those that are associated with hereditary cancer syndromes, can be inherited from a person’s parents. Inherited mutations play a major role in the development of about 5% to 10% of all cancers. Inherited genetic mutations can increase a person’s risk of developing cancer; however, a cancer-predisposing mutation does not necessarily mean that everyone who inherits the mutation will develop cancer. Several factors influence the outcome in a given person with the mutation. The list below includes some of the more common inherited cancer syndromes:

  • Gene: APC
  • Related cancer types: Colorectal cancer, multiple non-malignant colon polyps, and both benign and cancerous tumors in the small intestine, brain, stomach, bone, skin.
  • Gene: MEN1
  • Related cancer types: Pancreatic endocrine tumors and (usually benign) parathyroid and pituitary gland tumors

Exogenous hormone use

Oral contraceptives[12]

  • The results of population studies to examine associations between oral contraceptive use and cancer risk have not always been consistent.

Menopausal hormone therapy[13]

The most comprehensive evidence about risks and benefits of MHT comes from two randomized clinical trials that were sponsored by the National Institutes of Health as part of the Women’s Health Initiative (WHI): The WHI Estrogen-plus-Progestin Study, in which women with a uterus were randomly assigned to receive either a hormone medication containing both estrogen and progestin or a placebo and The WHI Estrogen-Alone Study, in which women without a uterus were randomly assigned to receive either a hormone medication containing estrogen alone or a placebo.

  • The breast cancers in these women were larger and more likely to have spread to the lymph nodes by the time they were diagnosed.
  • The number of breast cancers in this group of women increased with the length of time that they took the hormones and decreased after they stopped taking the hormones.
  • Among women who were diagnosed with lung cancer, women who took estrogen plus progestin were more likely to die of the disease than those who took the placebo.
  • Women who have had a hysterectomy and who use estrogen-alone MHT have a reduced risk of breast cancer that continues for at least 5 years after they stop taking MHT.
  • Women who take estrogen plus progestin have an increased risk of breast cancer that continues after they stop taking the medication.
  • Studies have documented a decline in breast cancer diagnoses in the United States after the sharp reduction in the use of MHT that followed publication of the initial results of the Estrogen-plus-Progestin Study in July 2002

Factors That May Affect the Risk of Cancer

Diet[1]

[1]

Alcohol

Information below is based on the National Cancer Institute Alcohol and Cancer Risk page.[14]

  • Based on extensive reviews of research studies, there is a strong consensus about the association between alcohol drinking and several types of cancer.
  • The National Toxicology Program of the US Department of Health and Human Services lists consumption of alcoholic beverages as a known human carcinogen.
  • Evidence indicates that the more alcohol a person drinks -particularly the more alcohol a person drinks regularly over time- the higher his or her risk of developing an alcohol-associated cancer.
  • Drinking alcohol is related with an increased risk of the following types of cancers:
  • Head and neck cancer: Alcohol consumption is a major risk factor for certain head and neck cancers, particularly cancers of the oral cavity, pharynx, and larynx.
  • People who consume 50 or more grams of alcohol per day (approximately 3.5 or more drinks per day) have at least a two to three times greater risk of developing these cancers than nondrinkers.
  • The risks of these cancers are substantially higher among persons who consume this amount of alcohol and also use tobacco.
  • Esophageal cancer: Alcohol consumption is a major risk factor for esophageal squamous cell carcinoma. People who inherit a deficiency or polymorphisms in ALDH2 (an enzyme that metabolizes alcohol) have been found to have substantially increased risks of alcohol-related esophageal squamous cell carcinoma.[15][16]
  • Breast cancer: More than 100 epidemiologic studies have looked at the association between alcohol consumption and the risk of breast cancer in women. ::* These studies have consistently found an increased risk of breast cancer associated with increasing alcohol intake. A meta-analysis of 53 of these studies (which included a total of 58,000 women with breast cancer) showed that women who drank more than 45 grams of alcohol per day (approximately three drinks) had 1.5 times more risk of developing breast cancer as nondrinkers.
  • The risk of breast cancer was higher across all levels of alcohol intake: The Million Women Study in the United Kingdom showed an estimate of breast cancer risk at low to moderate levels of alcohol consumption: every 10 grams of alcohol consumed per day was associated with a 12 percent increase in the risk of breast cancer.
  • Colorectal cancer: Alcohol consumption is associated with a modestly increased risk of cancers of the colon and rectum.
  • A meta-analysis of 57 cohort and case-control studies that examined the association between alcohol consumption and colorectal cancer risk showed that people who regularly drank 50 grams or more of alcohol per day (approximately 3.5 drinks) had 1.5 times the risk of developing colorectal cancer as nondrinkers or occasional drinkers.
  • For every 10 grams of alcohol consumed per day, there was a small 7% increase in the risk of colorectal cancer.
  • Multiple studies have shown that increased alcohol consumption is associated with a decreased risk renal cell carcinoma and Non-Hodgkin's Lymphoma (NHL). A meta-analysis of the NHL studies found a 15% lower risk of NHL among alcohol drinkers compared with nondrinkers. The mechanisms by which alcohol consumption would decrease the risks of either renal cell carcinoma or NHL are not understood.

Pregnancy

Information below is based on the National Cancer Institute Reproductive History and Breast Cancer Risk page.[17]

Studies have shown that a woman’s risk of developing breast cancer is related to her exposure to hormones that are produced by her ovaries (estrogen and progesterone). Reproductive factors that increase the duration and/or levels of exposure to ovarian hormones, which stimulate cell growth, have been associated with an increase in breast cancer risk. Pregnancy and breastfeeding both reduce a woman’s lifetime number of menstrual cycles, and thus her cumulative exposure to endogenous hormones. In addition, pregnancy and breastfeeding have direct effects on breast cells, causing them to differentiate, or mature, so they can produce milk. Some factors related to pregnancy may increase the risk of breast cancer. These factors include the following:

  • Older age at birth of first child: Women who are older than 30 years-old when they give birth to their first child have a higher risk of breast cancer than women who have never given birth.
  • Recent childbirth: Women who have recently given birth have a short-term increase in risk that declines after about 10 years. The reason for this temporary increase is not known, but it is believed that it may be due to the effect of high levels of hormones on microscopic cancers or to the rapid growth of breast cells during pregnancy.
  • Taking diethylstilbestrol (DES) during pregnancy: Women who took DES during pregnancy have a slightly higher risk of developing breast cancer than women who did not take DES during pregnancy. Daughters of women who took DES during pregnancy may also have a slightly higher risk of developing breast cancer after age 40 than women who were not exposed to DES while in the womb.
  • Abortion and miscarriage: The evidence does not support early termination of pregnancy as a cause of breast cancer.[18]
  • Women who have had a full-term pregnancy have reduced risks of ovarian cancer and endometrial cancer. The risks of these cancers decline with each additional full-term pregnancy.

Physical Activity

Information below is based on the National Cancer Institute Cancer Prevention Overview: Risk Factors page.[1]

Studies have shown that physically active people have a lower risk of certain cancers than those who are not. It is not known if physical activity itself is the reason for this. Physical activity has been associated with a lower risk of the following cancers:

Obesity

Information below is based on the National Cancer Institute Cancer Prevention Overview: Risk Factors page.[1]

  • Studies show that obesity is linked to a higher risk of the following types of cancer:
  • It is not known if losing weight lowers the risk of cancer

Environmental Risk Factors

Information below is based on the National Cancer Institute Cancer Prevention Overview: Risk Factors page.[1]

Being exposed to chemicals and other substances in the environment has been linked to some cancers:

  • Air pollution as a cancer risk factor has been demonstrated. These includes:
  • Association between lung cancer and secondhand smoke, outdoor air pollution, and asbestos
  • Association between drinking water that contains a large amount of arsenic and skin cancer, bladder cancer, and lung cancer
  • There are inconclusive results from studies performed to see if pesticides and other pollutants increase the risk of cancer. The results of those studies have been unclear because other factors can change the results of the studies.

References

  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 National Cancer Institute: PDQ® Cancer Prevention Overview. Bethesda, MD: National Cancer Institute. Date last modified 04/17/2014. Available at:http://www.cancer.gov/cancertopics/pdq/prevention/overview/patient.
  2. National Cancer Institute: PDQ® Cancer Prevention Overview. Bethesda, MD: National Cancer Institute. Available at:http://www.cancer.gov/cancertopics/factsheet/Risk/hiv-infection.
  3. National Cancer Institute: PDQ® Cancer Prevention Overview. Bethesda, MD: National Cancer Institute. Available at:http://www.cancer.gov/cancertopics/factsheet/Risk/HPV.
  4. National Cancer Institute: PDQ® Cancer Prevention Overview. Bethesda, MD: National Cancer Institute. Available at:http://www.cancer.gov/cancertopics/factsheet/Risk/h-pylori-cancer.
  5. National Cancer Institute: PDQ® Cancer Prevention Overview. Bethesda, MD: National Cancer Institute. Date last modified 04/17/2014. Available at:http://www.cancer.gov/cancertopics/factsheet/Risk/cellphones.
  6. National Cancer Institute: PDQ® Cancer Prevention Overview. Bethesda, MD: National Cancer Institute. Date last modified 04/17/2014. Available at:http://www.cancer.gov/cancertopics/factsheet/Risk/asbestos.
  7. National Cancer Institute: PDQ® Cancer Prevention Overview. Bethesda, MD: National Cancer Institute. Date last modified 04/17/2014. Available at:http://www.cancer.gov/cancertopics/factsheet/Risk/formaldehyde.
  8. National Cancer Institute: PDQ® Cancer Prevention Overview. Bethesda, MD: National Cancer Institute. Date last modified 04/17/2014. Available at:http://www.cancer.gov/cancertopics/factsheet/Risk/hair-dyes.
  9. National Cancer Institute: PDQ® Cancer Prevention Overview. Bethesda, MD: National Cancer Institute. Date last modified 04/17/2014. Available at:http://www.cancer.gov/cancertopics/factsheet/Risk/acrylamide-in-food.
  10. National Cancer Institute: PDQ® Cancer Prevention Overview. Bethesda, MD: National Cancer Institute. Available at:http://www.cancer.gov/cancertopics/factsheet/Risk/artificial-sweeteners.
  11. National Cancer Institute: PDQ® Cancer Prevention Overview. Bethesda, MD: National Cancer Institute. Available at:http://www.cancer.gov/cancertopics/factsheet/Risk/genetic-testing.
  12. National Cancer Institute: PDQ® Cancer Prevention Overview. Bethesda, MD: National Cancer Institute. Available at:http://www.cancer.gov/cancertopics/factsheet/Risk/genetic-testing.
  13. National Cancer Institute: PDQ® Cancer Prevention Overview. Bethesda, MD: National Cancer Institute. Available at:http://www.cancer.gov/cancertopics/factsheet/Risk/menopausal-hormones.
  14. National Cancer Institute: PDQ® Cancer Prevention Overview. Bethesda, MD: National Cancer Institute. Available at:http://www.cancer.gov/cancertopics/factsheet/Risk/alcohol.
  15. Zhang GH, Mai RQ, Huang B (2010). "Meta-analysis of ADH1B and ALDH2 polymorphisms and esophageal cancer risk in China". World J Gastroenterol. 16 (47): 6020–5. PMC 3007115. PMID 21157980.
  16. Brooks PJ, Enoch MA, Goldman D, Li TK, Yokoyama A (2009). "The alcohol flushing response: an unrecognized risk factor for esophageal cancer from alcohol consumption". PLoS Med. 6 (3): e50. doi:10.1371/journal.pmed.1000050. PMC 2659709. PMID 19320537.
  17. National Cancer Institute: PDQ® Cancer Prevention Overview. Bethesda, MD: National Cancer Institute. Available at:http://www.cancer.gov/cancertopics/factsheet/Risk/reproductive-history.
  18. National Cancer Institute: PDQ® Cancer Prevention Overview. Bethesda, MD: National Cancer Institute. Available at:http://www.cancer.gov/cancertopics/factsheet/Risk/abortion-miscarriage.



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