Carcinoma of Unknown Primary

Definition

Cancer of unknown primary (CUP) is a rare condition in which cancer cells are found in the body, but the site where the cancer began (the primary tumor) cannot be identified, even after extensive testing.

Characteristics

CUP can affect lymph nodes, liver, lungs, bones, or other organs. The cancer has already spread (metastasized) when it’s discovered. Because the origin is unknown, CUP is classified based on the location of metastases and the type of cancer cells found.

Diagnosis and Prognosis

Diagnosis includes imaging tests, biopsies, and advanced pathology techniques, including immunohistochemistry and molecular testing, to narrow down the likely origin. Prognosis depends on the type of cancer cells, where the cancer has spread, and the patient’s response to treatment. Some CUP cases respond well to therapy when their profile resembles known, treatable cancers.

Treatment

Treatment is often based on the most likely site of origin and may include chemotherapy, radiation therapy, hormone therapy, or targeted therapy. Molecular profiling is increasingly used to personalize treatment strategies.

Last Revised: 12 May , 2025