Carcinoma of unknown primary (CUP) refers to a type of cancer where the site of origin of the primary tumor cannot be identified, meaning the cancer has metastasized or spread to other parts of the body without a clear source. CUP accounts for around 3-5% of all cancer diagnoses.
CUP is often diagnosed when a patient presents with metastatic cancer, but the primary tumor cannot be located despite extensive evaluation. In some cases, the primary tumor may have regressed or resolved on its own, making identification difficult.
