Canadian Cancer Society logo

Cancer of unknown primary

You are here: 

Risk factors for cancer of unknown primary

Any substance or condition that increases cancer risk is referred to as a risk factor. Cancer of unknown primary (CUP) is a cancer that has already spread (metastasized) when it is found, but doctors don’t know where it started (primary tumour). CUP is not a single type of cancer, but a group of many different types of cancer. Different factors can increase the risk for different types of cancer. This makes it very hard to identify specific risk factors for CUP.

In some cases of CUP, the primary cancer is eventually found. Knowing the type of primary tumour can make it easier to identify factors that are known to develop or may increase the risk of developing that type of cancer.

  • Researchers have found that many cancers of unknown primary started in the lung, pancreas, kidney, head and neck area or the esophagus. We know that smoking increases the risk for all of these cancers.
  • Other CUPs are found to have started in the colon and rectum, stomach or ovaries. Diet, physical activity and body weight are known to affect a person’s risk for developing these cancers. However, even if people with CUP have one or more of the risk factors for these cancers, it’s not possible to know for sure if they had a role in causing their cancer.

CUP is more frequently diagnosed in people around age 60.

See a list of questions to ask your doctor about risks.


Dr David Hammond E-cigarettes in Canada

Read more

Access to services in your community

Illustration of houses side-by-side

The Canadian Cancer Society’s Community Services Locator helps cancer patients and their families find the services and programs they need in their community.

Learn more