What is carcinoma of unknown primary (CUP)?

What is carcinoma of unknown primary (CUP)?

Carcinoma of unknown primary (CUP) is a diagnosis given when cancer is found in your body but it’s not known where the original cancer started.

Cancer can start in any tissue in your body. Where it first starts — the primary location — defines the cancer. In other words, if cancer begins in your liver and spreads (metastasizes) to your lung, it’s still called liver cancer and not lung cancer.

Cells of your tissues and organs have features that are unique to that tissue and other features that are shared by several tissue types. Features are things like the size and shape of the cells, their DNA and cell arrangement. Knowing various cell types helps doctors recognize healthy cells and cancer cells. Cancer changes the usual appearance of a cell type. Doctors can determine that cancer has spread when they find abnormal cell types in another part of your body where they don’t belong (for example, finding abnormal liver cells in your lung tissue).

Sometimes when cancer spreads to another area of your body and the abnormal cell features don’t lead to finding where cancer first started, the cancer is called carcinoma of unknown primary (CUP). It’s also known as occult primary tumor.