What is cancer of unknown primary?

Cancer occurs when abnormal cells within the body grow in an uncontrolled way. Cancer can form in any of the body’s tissues. The first cancer that develops is called the primary cancer. Cancer can then spread elsewhere in the body. When cancer spreads to another part of the body, this is called the secondary cancer. Read More

Sometimes, the secondary cancer is found but the primary cancer cannot be found. This is called cancer of unknown primary.

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 detected.
  • The body’s immune system may have killed the primary cancer.
  • The primary cancer may already have been removed by surgery for another condition. Hide