Cancer of an unknown primary site (CUPS) is a metastatic tumor with no obvious source. It is detected by a biopsy that shows cancer from a part of the body that does not produce that type of malignancy, and no site of origin is identified despite a thorough physical examination, blood tests, x-rays and other imaging studies.
No primary site of origin can be identified in 2 to 9 percent of patients diagnosed with metastatic cancer. This is often because the primary tumor is so small that it is undetectable or the primary site is difficult to see directly or by using imaging techniques.
Since by definition the disease is diagnosed at a metastatic stage, the prognosis is generally poor. A significant percentage of patients, however, can have symptoms relieved and can occasionally be cured. For example, germ cell tumors, choriocarcinoma , lymphoma and certain sarcomas are potentially curable even in their metastatic stages. Other tumors such as prostate cancer, breast cancer and endometrial carcinoma are amenable to hormonal therapy.
Unfortunately, the most common origins of CUPS are lung and pancreatic cancers. These two tumors are generally incurable at the metastatic stage, with an average survival of about three or four months and with only 25 percent and 10 percent alive after one and five years respectively.
