Cancer of unknown primary origin

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Cancer of unknown primary origin (CUP) is a cancer that is determined to be at the metastatic stage at the time of diagnosis, but a primary tumor cannot be identified. A diagnosis of CUP requires a clinical picture consistent with metastatic disease and one or more biopsy results inconsistent with a tumor cancer.

CUP is found in about 3 to 5% of all people diagnosed with invasive cancer,^[1] and carries a poor prognosis in most (80 to 85%) of those circumstances. The other 15 to 20% of patients, however, have a relatively long survival with appropriate treatment.^[1]