A risk factor is anything that increases a person's chance of getting a disease such as cancer. Risk factors can be lifestyle-related, environmental, or genetic (inherited). Different cancers have different risk factors. But having a risk factor, or even several, does not mean that a person will get the disease.

• Lifestyle-related risk factors for some types of cancer include such things as smoking, an unhealthy diet, or unprotected exposure to strong sunlight.

• Environmental risk factors are influences in our surroundings such as high levels of radiation, cancer-causing chemicals, and certain infections.

• Genetic risk factors are inherited from a parent. Most people with a cancer caused by an inherited tendency have several close blood-relatives with cancer. Members of these families often have a very high risk of developing cancer. The vast majority of cancers, however, are not caused by genetic risk factors. If a patient has several family members with cancer, genetic testing may be considered. Blood tests can detect some of the inherited DNA changes responsible for the high risk of breast, ovarian, colorectal, or thyroid cancer in some families.

Each type of cancer has distinct risk factors. Since the exact type of a cancer of unknown primary is not known, it is difficult to identify the risk factors. Also, these cancers are a very diverse group, making this issue even more complicated. But there is some research that provides some information about CUP risk factors. If patients who have died of a cancer of unknown primary have an autopsy (examination of organs to find the cause of death), the source of the cancer is sometimes found.

Smoking is probably an important risk factor for CUP. Over half of patients have a history of smoking. When autopsy studies are done, many of these cancers are found to have started in the pancreas, lungs, kidneys, throat, larynx, or esophagus. Smoking increases the risk for all of these cancers, especially those in the lung, throat, and larynx.

Other cancers of unknown primary are eventually found to have started in the stomach, colon, or rectum and specific dietary risk factors are known to be associated with these cancers (For more information, see our documents on these cancers.)

Malignant melanoma (an aggressive type of skin cancer) is another source of cancer of unknown primary. The most important melanoma risk factor is unprotected exposure to ultraviolet radiation in sunlight.

Revised: 08/02/2006