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Carcinoma of unknown primary, a diagnosis that deserves a specialist team.

When metastatic cancer is found but the source cannot be identified, modern pathology, molecular profiling and a dedicated CUP MDT change what is possible.

A radiographer guides a patient onto the bed of an advanced 3 Tesla MRI scanner in a London imaging suite

Why trust this guide

  • 01

    Editorial team

    Written by our editorial team from the UK sources listed on each page.

  • 02

    Sourced from guidance

    Checked against NICE CG104, ESMO and specialist CUP service standards you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK practice including molecular profiling, tissue-of-origin assays and immunotherapy for MSI-H CUP.

Key facts

CUP at a glance.

The essentials, in plain English: what CUP is, how common it is, and how the UK approaches diagnosis and treatment.

  • What it is

    Metastatic malignant disease where the primary tumour cannot be identified despite a thorough diagnostic workup.

  • How common

    Around 3 to 5 per cent of all cancers, with a median age at diagnosis in the 60s.

  • Prognosis

    Overall poor, with median survival often measured in months, but heterogeneous with favourable subgroups doing much better.

  • Presentation

    Non-specific symptoms, site-specific metastatic disease, incidental imaging finding or oncological emergency.

  • Workup

    Guided by NICE CG104 and ESMO, combining history, exam, bloods, targeted imaging, core biopsy, IHC and molecular profiling.

  • Treatment

    Treat as the specific cancer when a favourable subgroup is identified, otherwise empirical chemotherapy plus molecularly matched therapy.

Why this guide matters

A modern, specialist-led approach to CUP.

CUP is heterogeneous. The three points below shape everything else on this page and can meaningfully change outcomes.

  • Favourable subgroups matter

    Careful workup identifies subgroups (breast, ovarian, head and neck, germ cell, prostate, MSI-H) that should be treated as those cancers, with much better outcomes.

  • Molecular profiling changes plans

    Comprehensive genomic profiling and tissue-of-origin assays are increasingly used to guide targeted therapy and immunotherapy.

  • Specialist CUP MDTs are essential

    Dedicated UK CUP services at the Royal Marsden, Christie, UCLH, Nottingham and Sheffield bring the expertise these cases need.

How the diagnosis is made

From first scan to a specialist plan.

The steps a UK oncologist and CUP MDT will normally follow, in order, so you know what to expect and why.

  1. 01

    Assessing

    History and full physical exam

    Systematic review with breast, pelvic, rectal, skin, lymph node, oral cavity and testicular examination to reveal an occult primary.

  2. 02

    Assessing

    Baseline bloods and tumour markers

    FBC, LFTs, U&Es, calcium, LDH, ALP plus a focused marker panel: CEA, CA 19-9, CA 125, AFP, beta-hCG, PSA in men, CA 15-3 and thyroglobulin where relevant.

  3. 03

    Assessing

    CT chest, abdomen and pelvis

    First-line imaging to map metastatic disease and look for a primary. MRI, PET-CT, mammography, gynae imaging, testicular US and endoscopy are added selectively.

  4. 04

    Confirming

    Core biopsy of a metastasis

    A core biopsy is preferred to fine-needle aspiration so the histopathologist has enough tissue for full IHC and molecular work.

  5. 05

    Confirming

    Immunohistochemistry panel

    IHC distinguishes adenocarcinoma, squamous, melanoma, lymphoma, germ cell, neuroendocrine and sarcoma, and points to a likely site of origin.

  6. 06

    Planning

    Molecular and tissue-of-origin assay

    Comprehensive genomic profiling, tissue-of-origin assays such as CancerType ID, Tempus or Foundation One, MSI, TMB, HER2, BRAF, ALK, EGFR and NTRK.

  7. 07

    Planning

    Specialist CUP MDT review

    A dedicated CUP MDT integrates clinical, radiological, pathological and molecular data, and directs any further targeted investigations.

Typical timeline: first presentation to a settled specialist plan in weeks.

Symptoms

How CUP tends to present.

Presentations range from vague weight loss and fatigue to site-specific metastatic disease, incidental scan findings and, sometimes, an oncological emergency.

  • Non-specific symptoms

    Weight loss, fatigue, anorexia and general malaise are common and often precede a specific finding.

  • Hepatomegaly and liver metastases

    An enlarged, hard or tender liver, sometimes with jaundice or deranged liver function, points to hepatic spread.

  • Lymphadenopathy

    Cervical, axillary, inguinal or supraclavicular (Virchow) nodes may be the first clue and are often biopsied to make the diagnosis.

  • Bone pain and bone metastases

    Persistent, worsening or night pain, often with raised alkaline phosphatase, suggests bony spread.

  • Ascites or pleural effusion

    Fluid in the abdomen or chest, with breathlessness or abdominal distension, can be the presenting problem.

  • Neurological features

    Brain metastases, spinal cord compression or leptomeningeal disease may present with headaches, weakness or new neurological deficit.

  • Incidental finding

    Metastatic disease is sometimes picked up on imaging or a biopsy done for another reason.

  • Red flag - oncological emergency

    Spinal cord compression, hypercalcaemia, pulmonary embolism or major haemorrhage need immediate hospital assessment.

Treatment

How CUP is treated in the UK.

Treatment follows the identified subgroup where possible, and combines chemotherapy, molecularly matched therapy, immunotherapy, local treatment and supportive care.

  • Treat as the identified primary

    If workup points to a favourable subgroup, treatment follows that cancer pathway rather than a generic CUP protocol.

  • Empirical chemotherapy

    For unfavourable adenocarcinoma CUP, carboplatin-paclitaxel or gemcitabine-based regimens give response rates of around 20 to 40 per cent.

  • Immunotherapy

    Pembrolizumab is used for MSI-H CUP (KEYNOTE-158) and is being evaluated in PD-L1 high CUP, including trials such as CUPISCO.

  • Molecularly targeted therapy

    BRAF, NTRK, HER2 and ALK inhibitors are used when comprehensive genomic profiling identifies an actionable driver.

  • Surgery and radiotherapy

    Local treatment is used for a resectable single metastasis, symptomatic bone or brain disease and cord compression.

  • Specialist CUP service referral

    UK centres including the Royal Marsden, Christie, UCLH, Nottingham and Sheffield run dedicated CUP MDTs.

  • Palliative and supportive care

    Specialist symptom control, hospice input and advance care planning are integral throughout, not just at the end.

  • Charity and peer support

    Cancer Research UK, Macmillan and the CUP Foundation provide information, financial guidance and peer support.

What this guide is based on

The sources behind every claim on this page.

UK national guidance and specialist society standards, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your oncologist knows your case and your imaging. If in doubt, ask about referral to a specialist CUP service.

  • NICE. Metastatic malignant disease of unknown primary origin in adults (CG104).

  • ESMO. Clinical practice guideline on cancers of unknown primary site.

  • Royal College of Pathologists. Dataset for histopathological reporting of CUP.

  • MHRA and NHS England commissioning guidance on molecular profiling and immunotherapy.

Red flags

When CUP needs urgent attention.

These situations are oncological emergencies and need same-day hospital review, not a wait for an outpatient appointment.

  • Spinal cord compression

    New back pain with leg weakness, sensory change or bladder or bowel disturbance needs urgent MRI and oncology input the same day.

  • Hypercalcaemia

    Confusion, drowsiness, thirst, constipation or dehydration with a raised corrected calcium is an emergency needing IV fluids and bisphosphonates.

  • Pulmonary embolism

    Sudden breathlessness, pleuritic chest pain or unexplained tachycardia in a patient with cancer needs same-day assessment.

  • Major haemorrhage

    Significant bleeding from any site in a patient with metastatic disease is a hospital-level emergency.

  • Superior vena cava obstruction

    Facial and neck swelling, distended veins and breathlessness need urgent imaging and oncology review.

  • Rapid clinical deterioration

    Fast weight loss, jaundice, worsening confusion or falls in a patient with a suspected CUP diagnosis needs urgent review.

  • Neutropenic sepsis

    Fever within six weeks of chemotherapy is an emergency, even without an obvious source.

  • Uncontrolled pain

    Severe or escalating pain, especially spinal or bony, needs urgent assessment and specialist palliative input.

  • Suicidal ideation or crisis

    A CUP diagnosis carries huge psychological weight. Any crisis or suicidal thoughts need immediate mental-health support.

Living with it

A difficult diagnosis, handled by a specialist team.

Four things that make the biggest difference: a specialist CUP MDT, modern molecular testing, early palliative input and the charities that exist to help you.

A quiet reminder

Second opinions are welcome and expected.

CUP is unusual and fast-moving. A specialist CUP centre will often support your local team rather than replace them.

  1. 01 Team

    Insist on a CUP MDT

    A specialist CUP service brings pathology, molecular expertise and oncology together and often changes the plan.

  2. 02 Testing

    Ask about molecular profiling

    Comprehensive genomic and tissue-of-origin testing can uncover a favourable subgroup or an actionable target such as NTRK, BRAF, HER2 or MSI-H.

  3. 03 Support

    Bring in palliative care early

    Early specialist symptom control is linked to better quality of life and does not mean giving up on treatment.

  4. 04 Community

    Use the charities

    Cancer Research UK, Macmillan and the CUP Foundation offer information, financial guidance and peer contact that can make a real difference.

Frequently asked

Everything we get asked about CUP.

Quick answers on workup, favourable subgroups, molecular profiling and treatment.

  • What is carcinoma of unknown primary?

    Carcinoma of unknown primary, or CUP, is metastatic cancer where the original site cannot be identified despite a thorough workup. It accounts for around 3 to 5 per cent of all cancers and is usually diagnosed in the 60s.

  • Why can’t the primary always be found?

    Some primaries are very small, have regressed, or sit in areas that are hard to image. Modern immunohistochemistry, molecular profiling and tissue-of-origin assays now identify a likely site in many cases that would previously have stayed unknown.

  • What is the prognosis?

    Overall, prognosis is poor and median survival for unfavourable subgroups is often measured in months. However, CUP is heterogeneous and favourable subgroups, such as women with adenocarcinoma in axillary nodes treated as breast cancer, can have prolonged survival.

  • What are favourable subgroups?

    These include women with adenocarcinoma in axillary nodes (treated as breast cancer), women with peritoneal serous carcinoma (treated as ovarian), squamous cell carcinoma in cervical nodes (treated as head and neck), poorly differentiated midline carcinoma (germ cell), neuroendocrine CUP, single resectable metastases, men with osteoblastic bone metastases and raised PSA (treated as prostate), and MSI-H CUP which responds to immunotherapy.

  • What is empirical chemotherapy?

    When no favourable subgroup is found, unfavourable adenocarcinoma CUP is often treated with combinations such as carboplatin-paclitaxel or gemcitabine-based regimens. Response rates are around 20 to 40 per cent and median survival is typically 6 to 9 months.

  • Where can I get specialist CUP care in the UK?

    Dedicated CUP services and MDTs are available at centres including the Royal Marsden, the Christie, UCLH, Nottingham and Sheffield. Ask your oncologist for a referral or second opinion if a specialist CUP team is not already involved.

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