What is cancer of unknown primary?

People with CUP often have more than one secondary cancer. It’s more common in older people|, but people in their 40s and 50s can also get CUP. 

Your doctor may suspect you have CUP if early tests don’t find the primary cancer. But the diagnosis won’t be certain until you’ve had all the appropriate tests. Doctors will try to find the primary cancer because it helps them plan the most effective treatment| for you. Some people with suspected CUP may be too unwell to have lots of tests.

Sometimes, tests will find the primary cancer. When this happens, the cancer is no longer called CUP. It’s named after the primary cancer and treated accordingly.

Even when the primary cancer can’t be found, your specialist may be able to suggest a probable part of the body where the cancer started. This will be based on your specialist’s experience, where the secondary cancers are, your symptoms| and test results. 

Why the primary cancer can’t be found

There are different reasons why a primary cancer can’t always be found:

• The secondary cancer or cancers have grown and spread very quickly, but the primary is still too small to be picked up on scans.
• The cancer has been growing in more than one area of the body for some time, making it difficult to see where it started.
• The primary cancer might have disappeared, even though it has spread to other parts of the body.