Cancer of unknown primary origin

Cancer of unknown primary origin, abbreviated CUP, is a cancer that is already at the metastatic stage when it is diagnosed but whose primary tumor cannot be identified. Diagnosis needs a clinical picture consistent with metastatic disease together with biopsy results that do not point to a single primary tumor. CUP is found in about 3 to 5 percent of all people diagnosed with invasive cancer and carries a poor prognosis in most cases, 80 to 85 percent, while the remaining 15 to 20 percent have localized or small metastatic sites and relatively long survival with suitable treatment. The worldwide incidence is estimated at 2 to 15 cases per 100,000 person years and is declining as imaging and molecular markers make a primary tumor easier to find. Risk factors resemble those of other cancers, including tobacco use, alcohol misuse, family history and diabetes. Treatment is usually empirical chemotherapy, most often a platinum agent with paclitaxel or gemcitabine.