Canadian Cancer Society logo

Cancer of unknown primary

You are here: 

Risk factors for cancer of unknown primary

A risk factor is something that increases the risk of developing cancer. It could be a behaviour, substance or condition. Most cancers are the result of many risk factors, but it is very hard to know what the specific risks are for cancer of unknown primary (CUP). This is because CUP is cancer that had already spread before it was found, but doctors don’t know where it started in the body. So CUP may have the same risk factors 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 the age of 60.


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


Diet, lack of physical activity and being overweight or obesemay affect your risk for CUP. This is because CUP can start as colorectal, stomach or ovarian cancer. Eating certain foods, not getting enough exercise or being overweight or obese can increase your risk for these types of cancer.

Questions to ask your healthcare team

To make the decisions that are right for you, ask your healthcare team questions about risks.


Brock Taraba Brock has been cancer free for over a decade, thanks to the support we received from the Canadian Cancer Society.

Read Brock's story

Providing rides to cancer treatment

Illustration of car

For more than 50 years, the Canadian Cancer Society’s transportation program has enabled patients to focus their energy on fighting cancer and not on worrying about how they will get to treatment.

Learn more