Cancer of the unknown primary

Cancer of the unknown primary

Cancer of unknown primary, also known as CUP, describes cancer that has spread (metastatic), but it’s not known where in the body it started. The word ‘primary’ means the first place where the cancer started, and from where it has spread.

There are a number of reasons why it may not be possible to find the primary cancer:

• The primary cancer may be too small to be easily found.
• The body’s immune system may have killed the primary cancer.
• The primary cancer may already have been removed by surgery for another condition.

Cancer of unknown primary is a rare cancer. It is more common in older people than in younger people.