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Health condition · Clinically reviewed

Merkel cell carcinoma, a rare skin cancer that grows fast and needs urgent attention.

A firm, painless, rapidly enlarging nodule on sun-exposed skin is easy to dismiss as a cyst. It rarely is - and speed of diagnosis genuinely changes outcomes.

Jump to treatment
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Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Checked against NICE, BAD, ESMO and peer-reviewed sources you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK pathways including sentinel node biopsy, adjuvant radiotherapy and checkpoint immunotherapy.

Key facts

Merkel cell carcinoma at a glance.

The essentials, in plain English - what it is, who is at risk, and how it’s treated in the UK today.

  • What it is

    A rare, aggressive neuroendocrine skin cancer arising from Merkel cells, with a strong tendency to spread to lymph nodes and beyond.

  • Main cause

    Merkel cell polyomavirus is found in the majority of tumours - chronic UV damage is the other major driver.

  • Who gets it

    Older adults, median age around the 70s - risk rises sharply with immunosuppression, fair skin and heavy sun exposure.

  • How it looks

    A rapidly growing, firm, painless, red or purple nodule on sun-exposed skin - often mistaken for a cyst or insect bite.

  • Why speed matters

    Even a small primary lesion can already have spread to nearby lymph nodes by the time it is diagnosed.

  • Modern treatment

    Wide excision plus sentinel node biopsy and adjuvant radiotherapy, with checkpoint immunotherapy for advanced disease.

Why this guide matters

A rare cancer where early recognition changes everything.

Merkel cell carcinoma is uncommon, fast-moving and frequently misread as something benign. The three points below shape everything else on this page.

  • It grows fast, and spreads early

    Even a small, innocent-looking nodule can already carry regional lymph node involvement - this is why urgent referral matters.

  • Staging drives the whole plan

    Sentinel lymph node biopsy and staging imaging determine whether treatment stays local or needs to include the nodal basin and beyond.

  • Immunotherapy has changed outcomes

    Checkpoint inhibitors have transformed the outlook for advanced disease, exploiting the tumour’s strong immunogenicity.

How the diagnosis is made

From a suspicious lump to a staged plan.

The steps a UK dermatology and skin cancer team will normally follow, in order - so you know what to expect and why speed matters.

  1. 01

    Assessing

    Urgent 2-week wait referral

    Any rapidly growing, firm skin nodule - particularly in an older or immunosuppressed patient - should trigger an urgent suspected-cancer referral.

  2. 02

    Assessing

    Clinical assessment

    A dermatologist examines the lesion using the AEIOU features - Asymptomatic, Expanding rapidly, Immunosuppression, Older than 50, UV-exposed site.

  3. 03

    Assessing

    Skin biopsy

    Excisional or incisional biopsy for histopathology and immunohistochemistry - the characteristic CK20 staining pattern helps confirm the diagnosis.

  4. 04

    Confirming

    Sentinel lymph node biopsy

    Given the high metastatic potential even for small primaries, sentinel node biopsy is used to stage the disease and guide further treatment.

  5. 05

    Confirming

    Staging imaging

    CT or PET-CT looks for regional and distant spread, informing the overall stage and treatment plan.

  6. 06

    Confirming

    MDT discussion

    Every case is discussed at a specialist skin cancer or dermato-oncology multidisciplinary team meeting before treatment begins.

  7. 07

    Preparing

    Treatment planning

    Surgery, radiotherapy, lymph node management and, where needed, immunotherapy are sequenced according to stage.

Typical timeline: urgent referral to a fully staged treatment plan within a small number of weeks.

Symptoms

What Merkel cell carcinoma actually looks like.

The AEIOU features that raise suspicion - and the reasons this cancer is so often missed at first glance.

  • Rapidly growing nodule

    A firm, painless lump that noticeably enlarges over weeks rather than months - the hallmark presenting feature.

  • Red, purple or skin-coloured

    Colour varies - it can look deceptively benign, which is part of why diagnosis is often delayed.

  • Sun-exposed sites

    Most commonly on the head, neck or extremities - areas with the greatest lifetime UV exposure.

  • Painless

    Unlike a boil or infected cyst, the lesion is usually painless despite its rapid growth.

  • Older age

    Most cases occur in people in their 70s and beyond, reflecting cumulative sun damage and immune ageing.

  • Immunosuppression as a risk factor

    Transplant recipients, people living with HIV and those with chronic lymphocytic leukaemia carry significantly higher risk.

  • Mistaken for benign lesions

    Often initially assumed to be a cyst or insect bite, which can delay the urgent referral it needs.

  • Red flag - early spread

    High propensity for regional lymph node and distant metastasis, even when the primary tumour looks small.

Treatment

How Merkel cell carcinoma is treated in the UK.

Surgery and staging come first, radiotherapy is used liberally given the recurrence risk, and immunotherapy has transformed advanced disease.

  • Wide local excision

    Surgical removal of the primary tumour with appropriate margins - specialist dermatological or plastic surgery.

  • Sentinel lymph node biopsy

    Identifies whether the disease has already reached the nearest lymph nodes, guiding whether further nodal treatment is needed.

  • Adjuvant radiotherapy

    Often recommended to the primary site and/or nodal basin even after clear surgical margins, given the high risk of recurrence.

  • Lymph node dissection

    Surgical clearance of the nodal basin when nodes are clinically involved or the sentinel node is positive.

  • Checkpoint immunotherapy

    Avelumab and pembrolizumab are established options for advanced or metastatic disease, reflecting the tumour’s strong immunogenicity.

  • Selective chemotherapy

    Historically used for advanced disease - now largely superseded by immunotherapy given its better outcomes and tolerability.

  • Regular surveillance

    Close follow-up with skin checks and clinical examination, reflecting the high rates of recurrence after initial treatment.

  • Sun protection and immune review

    Ongoing sun protection advice, and review of immunosuppressive medication where relevant, to reduce further risk.

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 dermatologist or oncologist knows your history and staging and can tell you which parts apply to you. If in doubt, get seen urgently.

  • NICE. Suspected cancer: recognition and referral (NG12) - skin cancer pathways.

  • British Association of Dermatologists (BAD). Guidelines for the management of Merkel cell carcinoma.

  • ESMO Clinical Practice Guidelines. Merkel cell carcinoma.

  • Skcin - The Karen Clifford Skin Cancer Charity. Patient information on rare skin cancers.

Red flags

When a skin lump needs urgent attention.

Most skin lumps are entirely benign. These are the features that mean this one might not be - and where urgent assessment is needed.

  • Rapid nodule growth

    Any skin lump that visibly enlarges over a few weeks needs urgent same-pathway assessment, not a watch-and-wait approach.

  • Immunosuppressed patients

    Transplant recipients and people with CLL or HIV have a much higher risk - any new or changing lesion warrants prompt review.

  • Painless firm nodule on sun-exposed skin

    A classic and easily missed presentation - painless does not mean benign in this context.

  • Palpable lymph nodes

    A new lump in a regional lymph node area alongside a skin lesion should raise suspicion of nodal spread.

  • Delayed presentation

    Lesions mistaken for cysts or insect bites for weeks to months are a recognised pattern - always reassess a "cyst" that keeps growing.

  • Systemic symptoms

    Unexplained weight loss, fatigue or new masses elsewhere alongside a skin lesion should prompt urgent staging.

  • Recurrence after treatment

    Merkel cell carcinoma has a high recurrence rate - any new lump near a treated site needs prompt specialist review.

  • Rapid deterioration on treatment

    New or worsening symptoms during immunotherapy or radiotherapy should be reported to the oncology team without delay.

Living with it

A rare cancer, with a clear surveillance plan.

Four things that make the biggest difference after treatment - knowing your own skin, keeping follow-up appointments, protecting your skin for good and using the support that exists for rare cancers.

A quiet reminder

Recurrence risk is real, but so is close surveillance.

Most recurrences happen early and are caught at routine follow-up - this is exactly why the appointments matter.

  1. 01 Vigilance

    Know your own skin

    Check surgical and radiotherapy sites, and nearby lymph node areas, regularly for any new lump or change.

  2. 02 Follow-up

    Keep every appointment

    Surveillance visits are frequent in the first two to three years because recurrence risk is highest then.

  3. 03 Sun

    Protect your skin for good

    Daily SPF, protective clothing and shade reduce the risk of new UV-driven skin cancers developing.

  4. 04 Support

    Ask about support services

    Skcin and your specialist nurse team can help with the practical and emotional side of a rare cancer diagnosis.

Frequently asked

Everything we get asked about Merkel cell carcinoma.

Quick answers on causes, risk, staging and modern treatment.

  • What is Merkel cell carcinoma?

    A rare but aggressive neuroendocrine skin cancer that arises from Merkel cells. It typically presents as a rapidly growing, firm, painless nodule on sun-exposed skin and has a high tendency to spread to lymph nodes and beyond, even when the primary tumour is small.

  • What causes Merkel cell carcinoma?

    Most cases are strongly associated with Merkel cell polyomavirus, which is found in the majority of tumours. Chronic ultraviolet exposure is the other major driver, particularly in fair-skinned people with extensive lifetime sun exposure.

  • Who is most at risk?

    Older adults, typically in their 70s, carry the highest risk. Immunosuppression significantly increases risk - this includes organ transplant recipients, people living with HIV and those with chronic lymphocytic leukaemia - alongside fair skin and heavy UV exposure.

  • What does the AEIOU mnemonic mean?

    It summarises the typical features that should raise suspicion - Asymptomatic, Expanding rapidly, Immunosuppression, Older than 50, and a UV-exposed site. It is a helpful prompt for early recognition, though not every case shows all five features.

  • Why is a sentinel lymph node biopsy needed even for a small lesion?

    Merkel cell carcinoma has a high propensity for regional lymph node spread that can occur before the primary tumour looks concerning in size. Sentinel node biopsy checks for this spread and directly guides whether further nodal treatment, such as dissection or radiotherapy, is needed.

  • What treatments are available for advanced disease?

    Checkpoint immunotherapy - avelumab and pembrolizumab - is now the established treatment for advanced or metastatic Merkel cell carcinoma, reflecting the tumour’s strong immunogenicity linked to its viral and UV origins. Chemotherapy is still used selectively but has largely been superseded by immunotherapy due to better outcomes and tolerability.

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