In 2-5% of cancer diagnoses, a primary site of cancer can not be found. The patient becomes aware of a problem when a lymph node is found to be enlarged. The lymph node is removed and examined under a microscope. Even this careful examination will not identify where the cancer began. The lymph node is a secondary or metastatic site of the cancer. Other common sites of involvement of cancer of unknown primary site include liver, lung, bone and brain. In about half the cases, the primary site will eventually be discovered.

Treatment of CUPS is difficult and often based on the best guess of the primary site or of the likely behavior of the cancer. For example, in a patient with such a cancer found in a lymph node in the neck, radiation treatment aimed at possible primary sites in the head and neck is often used. In otherwise healthy patients with widespread metastatic CUPS, aggressive chemotherapy using multiple drugs or experimental therapies are considered. In patients with advanced disease and deteriorating health, palliative care aimed at control of symptoms is often the best course of therapy.

What is cancer of unknown primary site?