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Cancer of Unknown Primary (CUP)
Metastatic cancer confirmed by biopsy when the place where it first began cannot be identified after evaluation.
Understanding cancer of unknown primary
CUP is diagnosed when cancer is found in one or more parts of the body but tests do not establish its original site. It is not a single cancer type: pathology, imaging, clinical pattern and molecular tests are used to identify the most likely tumour family and treatments that may work. Sometimes the primary site remains unknown.
Possible signs and symptoms
- A persistent or enlarging lump
- Unexplained bone, abdominal or chest pain
- A lasting cough or shortness of breath
- Abdominal swelling or a persistent bowel change
- New neurological symptoms such as weakness or headaches
- Unexplained weight loss, fever or fatigue
Treatment and care
Treatment is based on pathology, where the cancer has spread, molecular findings, likely tissue of origin, overall health and whether the presentation belongs to a favourable subgroup.
Site-directed or local treatment
When tests strongly suggest a particular cancer type, treatment may follow that pathway. Surgery or radiation may be used for isolated or limited disease and certain favourable presentations.
Systemic treatment
Chemotherapy, immunotherapy or targeted therapy may be used according to tumour features and biomarkers. Supportive and palliative care are part of treatment planning.
Sources and medical information
Sources checked: 28 July 2026
CUP is a diagnosis made after biopsy and appropriate investigation; it cannot be identified from symptoms alone. Symptoms depend on where metastatic cancer is present. New neurological symptoms, breathing difficulty, severe pain or rapid deterioration need urgent medical care.
Official sources
Key Facts
MetastaticCancer is found away from its origin when CUP is diagnosed
Primary unknownThe original site remains unconfirmed after pathology and imaging evaluation