Cancer of Unknown Primary (CUP) may also be called Carcinoma of Unknown Primary Site or Occult Primary Cancer. This means that the cancer has already spread (metastasized) when it is found, but doctors do not know where it started (primary site). The metastatic tumour is found before the primary cancer is identified. The primary site may be identified after further testing, but the primary site is never found in many cases. CUP is also not a single type of cancer, but a group of different cancer types.