Stages of cancer of unknown primary

There is no staging system for cancer of unknown primary (CUP). This is because the cancer has already spread and doctors don’t know where the original cancer started. 

Doctors can usually group CUP by the type of cell the cancer started from. 

What is staging?

When someone is diagnosed with cancer, doctors usually carry out a number of tests to find out:

  • the size of the tumour 
  • whether it has spread to other parts of the body

This is called staging. It helps doctors decide on the best treatment plan.

Staging systems

Different cancer types have slightly different staging systems. So the stages used for bowel cancer are different from the stages used for breast cancer, for example.

For most types of cancer there are 4 number stages, from 1 to 4. Stage 1 is a small, localised tumour (early cancer). Cancer that has spread to another part of the body is stage 4 cancer (advanced cancer).

Staging system for CUP

With CUP, doctors don’t know where the original cancer started. So they can't accurately stage this type of cancer.

You usually still have several tests to find out where the cancer is. Your doctor uses all the information they can gather to help decide on your best treatment options.

The results of your scans and tests can often suggest the most likely place the cancer started.

Last reviewed: 
19 May 2021
Next review due: 
19 May 2024
  • Cancer and its Management (7th edition)
    J Tobias and D Hochhauser
    Wiley-Blackwell, 2015

  • Cancers of unknown primary site: ESMO clinical practice guidelines for diagnosis, treatment and follow up
    K Fizazi and others
    Annals of Oncology, 2015. Vol 26, Supplement 5

  • Principles and practice of oncology (9th edition)
    VT De Vita, TS Lawrence and SA Rosenberg
    Lippincott, Williams and Wilkins, 2011

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