Cancer of unknown primary site

Definition of cancer of unknown primary origin
National Cancer Institute

cancer of unknown primary origin

(KAN-ser ... UN-none PRY-mayr-ee OR-ih-jin)
A case in which cancer cells are found in the body, but the place where the cells first started growing (the origin or primary site) cannot be determined. Also called carcinoma of unknown primary and CUP.

Source: NCI Dictionary of Cancer Terms