Risks for cancer of unknown primary

Last medical review:

Certain behaviours, substances or conditions can affect your risk, or chance, of developing cancer. Some things increase your risk and some things decrease it. Most cancers are the result of many risks. But sometimes cancer develops in people who don't have any risks.

It is very hard to know what the specific risks are for cancer of unknown primary (CUP). This is because the cancer had already spread before it was found and doctors don't know where it started in the body. So CUP may have the same risks as different types of cancer.

Like many types of cancer, CUP most often affects older people. It is usually diagnosed in people who are around 60 years of age.

The following can increase your risk for CUP. There are things you can do to lower your risk and help protect yourself from developing cancer.

Smoking tobacco

Diet, exercise and excess weight

Sun and indoor tanning

Smoking tobacco

All forms of tobacco, including cigarettes, cigars, pipes and smokeless (spit) tobacco, may increase your risk for CUP.

In many cases doctors find out that CUP started as cancer of the lung, pancreas, kidney, esophagus or head and neck. Smoking tobacco is a risk factor for these types of cancer.

Learn more about how to live smoke-free.

Diet, physical activity and excess weight

CUP can start as colorectal, stomach or ovarian cancer. Not eating well, not getting enough physical activity and having overweight or obesity can increase your risk for these types of cancer.

Learn more about how to eat well, move more, sit less, and have a healthy body weight.

Sun and indoor tanning

The sun and indoor tanning equipment, such as tanning beds and sun lamps, increase your risk for CUP. Having a tan means that your skin has been damaged. The sun and indoor tanning can cause sunburns, premature aging, cataracts and skin cancers.

Learn more about how to be sun safe.

Understanding your cancer risk

To make the decisions that are right for you, ask your healthcare team questions about risks. Learn how cancer can be prevented and what you can do to reduce your risk.

Expert review and references

  • Canadian Cancer Society | Société canadienne du cancer
  • American Cancer Society . Cancer of Unknown Primary Risk Factors . 2018 : https://www.cancer.org/.
  • American Society of Clinical Oncology (ASCO). Unknown primary. Alexandria, VA.: 2008.
  • Cancer Research UK. Risks and Causes of CUP. 2020: https://www.cancerresearchuk.org/.
  • Pavlidis N, & Fizazi K . Carcinoma of unknown primary (CUP). Critical Reviews in Oncology/Hematology. Elsevier; 2009.
  • Pavlidis N, & Pentheroudakis G . Cancer of unknown primary site. Lancet. Elsevier; 2012.
  • Pentheroudakis G, Greco FA, Pavlidis N. . Molecular assignment of tissue of origin in cancer of unknown primary may not predict response to therapy or outcome: a systematic literature review. Cancer Treatment Reviews. Elsevier; 2009.
  • Tan WW . Medscape Reference: Metastatic Cancer With Unknown Primary Site . 2019 : https://www.medscape.com/oncology.