A set of genetic and environmental factors increase the risk of cancer.One of the important is family history.
Some families have a higher risk for certain cancers when compared with other families.

For example the risk of women for breast cancer increased 1,5-3 times when his mother or sister had breast cancer.

Some breast cancer associated with a specific genetic mutation, which is more often found in some ethnic groups and families.
Women with this gene mutation have a 80-90% chance of registration for breast cancer and 40-50% for ovarian cancer.
Researchers have found that 1% of Ashkenazi Jewish women have this gene mutation.

Other cancers that tend to be inherited in the family is skin cancer and colon cancer.

Chromosomal abnormalities increase the risk of cancer.
For example a person with Down's syndrome, which has a 3 pieces chromosome 21, have a risk of 12-20 times higher for acute leukemia.

A number of environmental factors increase the risk of cancer.
One of the most important is cigarette smoking. Cigarette smoking increases the risk of lung cancer, mouth, larynx (vocal cords) and the bladder.

From excessive exposure to ultraviolet light, particularly from the sun, causing skin cancer.

Ionizing radiation (which is carcinogenic) used in X-rays, generated from nuclear power plants and atomic bombs and can reach very long distances.
For example people who survived the atomic bomb dropped on Hiroshima and Nagasaki in World War II, has a high risk of occurrence of leukemia.

By uranium exposure in miners have been associated with the occurrence of lung cancer 10-20 years later, the higher the risk if the miners also smoked.

Long-term exposure to ionizing radiation affects a person to cancer of blood cells, including acute leukemia.

Food is another important risk factor for cancer, particularly cancers of the digestive tract.
High-fiber diet reduces the likelihood of colon cancer.
A diet that contains foods that are smoked and pickled (in the form of pickles) increase the risk of gastric cancer.
Reduce fat to less than 30% of total calories, will reduce the risk of colon cancer, breast and prostat.
Alcohol drinkers have a higher risk of throat cancer.

Many chemicals are known to cause cancer and other chemicals are suspected of many causes of cancer.
Exposure to certain chemicals may increase the risk of cancer after a few years later.
For example asbestos exposure can cause lung cancer and mesotelioma (pleural cancer).
These risks will be greater if the asbestos workers is also a cigarette smoker.

The risk of cancer also varies based on where a person lives.
Risk of colon cancer and breast cancer in Japan is low, but this increased risk in Japanese men living in America and will eventually have the same risk amount with the other American citizens.
The Japanese have an incidence rate of gastric cancer is very high, but the Japanese people who were born in America this figure is lower.
Geographical variations in cancer risk is likely to involve many factors, namely a combination of genetics, food and environment.

Some viruses cause cancer in humans and other viruses suspected of causing cancer.
Papilloma virus that causes genital warts is probably one of the causes of cervical cancer in women.
Cytomegalovirus causes Kaposi's sarcoma.
Hepatitis B virus can cause liver cancer, although carcinogens or promoters are not known.
In Africa, Epstein-Barr virus causes Burkitt's lymphoma, whereas in China these viruses cause nose and throat cancer. It was clear, that some additional factors (environmental or genetic), required for the occurrence of cancer caused by Epstein-Barr virus.
Some human retro virus, such as HIV virus, causes lymphoma and other blood cancers.

Infection by the parasite Schistosoma (Bilharzia) could cause bladder cancer because of the occurrence of chronic irritation of the bladder. But other chronic irritants do not cause cancer.