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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.

Many other factors in our environment, diet, and lifestyle may cause or prevent cancer. This summary reviews only the major cancer risk factors and protective factors that can be controlled or changed to reduce the risk of cancer. Risk factors that are not described in the summary include certain sexual behaviors, the use of estrogen, and being exposed to certain substances or chemicals.

Factors That are Known to Increase the Risk of Cancer

Tobacco

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

• Acute myelogenous leukemia (AML)
• Bladder cancer
• Esophageal cancer
• Kidney cancer
• Lung cancer
• Oral cancer
• Pancreatic cancer
• Stomach cancer

• Not smoking or quitting smoking lowers the risk of getting cancer and dying from cancer.
• Cigarette smoking causes about 30% of all cancer deaths in the United States.
• Cigarette smoking causes an estimated 443,000 deaths each year, including approximately 49,000 deaths due to exposure to secondhand smoke.
• Lung cancer is the leading cause of cancer death among both men and women in the United States, and 90 percent of lung cancer deaths among men and approximately 80 percent of lung cancer deaths among women are due to smoking.

Infections

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 papillomavirus (HPV):

• Cervical cancer
• Penis cancer
• Vaginal cancer
• Anal cancer
• Oropharyngeal cancer

• Hepatitis B and hepatitis C viruses increase the risk for liver cancer
• Epstein-Barr virus increases the risk for Burkitt lymphoma
• Helicobacter pylori increases the risk for gastric cancer

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

• Hepatitis B vaccine
• Human papillomavirus vaccine

Radiation

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

• Ultraviolet radiation from sunlight: This is the main cause of nonmelanoma skin cancers.
• Ionizing radiation including:

• Medical radiation from tests such as x-rays, CT scans, fluoroscopy, and nuclear medicine scans.
• Radon gas found in homes.

• 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:

• Leukemia
• Thyroid cancer
• Breast cancer in women
• Myeloma
• Lung cancer
• Gastric cancer
• Colon cancer
• Esophagueal cancer
• Bladder cancer
• Ovarian cancer

Immunosuppressive Medicines

Immunosuppressive medicines are linked to an increased risk of cancer. These medicines lower the body’s ability to stop cancer from forming. For example, immunosuppressive medicines may be used to keep a patient from rejecting an organ transplant.

Factors That May Affect the Risk of Cancer

Diet

The foods that you eat on a regular basis make up your diet. Diet is being studied as a risk factor for cancer. It is hard to study the effects of diet on cancer because a person’s diet includes foods that may protect against cancer and foods that may increase the risk of cancer.

It is also hard for people who take part in the studies to keep track of what they eat over a long period of time. This may explain why studies have different results about how diet affects the risk of cancer.

Some studies show that fruits and nonstarchy vegetables may protect against cancers of the mouth,esophagus, and stomach. Fruits may also protect against lung cancer.

Some studies have shown that a diet high in fat, proteins, calories, and red meat increases the risk ofcolorectal cancer, but other studies have not shown this.

It is not known if a diet low in fat and high in fiber, fruits, and vegetables lowers the risk of colorectal cancer.

See the following PDQ summaries for more information:

Breast Cancer Prevention Colorectal Cancer Prevention

Alcohol

Studies have shown that drinking alcohol is linked to an increased risk of the following types of cancers:

Oral cancer. Esophageal cancer. Breast cancer. Colorectal cancer (in men).

Drinking alcohol may also increase the risk of liver cancer and female colorectal cancer.

See the following PDQ summaries for more information:

Breast Cancer Prevention Colorectal Cancer Prevention Esophageal Cancer Prevention Oral Cancer Prevention Liver (Hepatocellular) Cancer Prevention

Physical Activity

Studies show that people who are physically active 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.

Studies show a strong link between physical activity and a lower risk of colorectal cancer. Some studies show that physical activity protects against postmenopausal breast cancer and endometrial cancer.

See the following PDQ summaries for more information:

Breast Cancer Prevention Colorectal Cancer Prevention Endometrial Cancer Prevention

Obesity

Studies show that obesity is linked to a higher risk of the following types of cancer:

Postmenopausal breast cancer. Colorectal cancer. Endometrial cancer. Esophageal cancer. Kidney cancer. Pancreatic cancer.

Some studies show that obesity is also a risk factor for cancer of the gallbladder.

It is not known if losing weight lowers the risk of cancers that have been linked to obesity.

See the following PDQ summaries for more information:

Breast Cancer Prevention Colorectal Cancer Prevention Endometrial Cancer Prevention Lung Cancer Prevention

Environmental Risk Factors

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

Links between air pollution and cancer risk have been found. These include links between lung cancer and secondhand tobacco smoke, outdoor air pollution, and asbestos. Drinking water that contains a large amount of arsenic has been linked to skin, bladder, and lung cancers.

Studies have been done 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.