What is CUP?

Primary cancer means where the cancer started. The part of the body where the cancer first started to grow is called the primary site. The cancer type is usually named after the part of the body where it first started to grow. For example, a cancer that starts in the lung is called a primary lung cancer.

A secondary cancer happens when cancer cells separate from a primary site and spread to another part of the body. The cancer cells travel through the blood or lymphatic system and form a new cancer somewhere else in the body.

A secondary cancer is also called a metastasis or metastatic cancer. It is made up of the same type of cancer cells that formed the primary cancer. For example, a cancer that starts in the lungs and spreads to the liver is made up of lung cancer cells, not liver cancer cells.

Cancer of unknown primary (CUP) means that your doctor is not sure where the cancer started. They have found a secondary cancer but have not been able to find the primary cancer. People with CUP sometimes have secondary cancer in more than 1 part of the body

With CUP, doctors cannot always tell which part of the body the cancer cells are from. But cancers are made up of different types of cells. These can be grouped based on the type of cells they are made up of. Knowing the type of cell can give the doctors a better idea about where the cancer may have started. This helps them to plan the best treatment.