Cancer of unknown primary origin

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 people, however, have localized or small metastatic sites at the time of diagnosis, and is associated with a relatively long survival with appropriate treatment.^[1]

The worldwide incidence of CUP is estimated to be 2-15 cases per 100,000 person years and this incidence is declining as advances are made in diagnostic imaging, molecular markers and other cancer diagnostic tests such that it is easier to find a primary tumor.^[2] Risk factors for CUP are similar to other types of cancers and include tobacco use, alcohol misuse, a family history of cancer, and diabetes.^[2]

Treatment usually involves empirical chemotherapy (most often with a platinum agent with paclitaxel or gemcitabine) but clinical data does not support the superiority of one drug or class over others.^[2]