What are the risk factors for cancer of unknown primary?

A risk factor is anything that increases a person’s chance of getting a disease such as cancer. Different cancers have different risk factors. For instance, smoking is a risk factor for lung cancer and many other cancers.

But risk factors don’t tell us everything. Having a risk factor, or even several, does not mean that a person will get the disease, and many people get cancer without having any known risk factors.

Since the exact type of cancer is not known for cancer of unknown primary (CUP), it is hard to say which risk factors apply. Smoking is likely an important risk factor for CUP. More than half of patients with CUP were smokers at one time. Autopsy studies (looking at organs to find the cause of death) of people who have died of CUP show that many of the cancers started in the pancreas, lungs, kidneys, throat, larynx, or esophagus. Smoking is a major risk factor for each of these cancers.

Other places CUP starts include the stomach, colon, or rectum. Diet, nutrition, and weight are risk factors linked to these cancers. A type of skin cancer called melanoma is another source of CUP. Too much unprotected exposure to sunlight is a risk factor for skin cancer.

But there are no factors that are known for certain to increase the risk of CUP. Even in people who may have one or more of the risk factors above, there is no way to know for sure if the factors are linked to the cancer.