What Is Merkel Cell Carcinoma?
Merkel cell carcinoma is a rare but aggressive neuroendocrine skin cancer, arising from cells in the deep layer of the epidermis. It is much rarer than BCC, SCC or melanoma, but has a higher tendency to recur locally and to spread to lymph nodes or distant sites, so it is treated with particular urgency once suspected.
Causes & Risk Factors
- Merkel cell polyomavirus (MCPyV) — implicated in the majority of cases
- Cumulative UV exposure — most lesions occur on sun-exposed skin
- Older age — Merkel cell carcinoma is uncommon under 50
- Immunosuppression — a significantly increased risk, including in organ transplant recipients and those with chronic lymphocytic leukaemia (CLL)
Signs to Look For — The "AEIOU" Features
Merkel cell carcinoma is often summarised by the mnemonic AEIOU, describing the typical presentation:
- Asymptomatic — usually painless
- Expanding rapidly — growing over weeks
- Immunosuppression — a relevant risk factor if present
- Older than 50 years of age
- UV-exposed site — most often the head, neck or limbs
It typically appears as a firm, red-purple or flesh-coloured nodule, painless, and growing noticeably over a matter of weeks.
Diagnosis & Staging
Diagnosis is confirmed by biopsy, including specific immunohistochemical staining (such as CK20 and Merkel cell polyomavirus markers) to distinguish it from other skin cancers and metastatic deposits. Because of its tendency to spread, staging investigations — including sentinel lymph node biopsy and, where indicated, cross-sectional imaging — are an important part of assessment once the diagnosis is confirmed.
Treatment
- Wide local excision — with margins typically of 1–2cm, planned individually based on the site and size of the lesion
- Sentinel lymph node biopsy — recommended for almost all patients given the high rate of nodal spread, even when lymph nodes appear clinically normal
- Adjuvant radiotherapy — frequently recommended even after complete surgical excision, given the high rate of local and regional recurrence associated with this cancer
- Multidisciplinary team (MDT) management — given its aggressive behaviour, Merkel cell carcinoma is managed jointly with oncology and, where relevant, radiotherapy colleagues from diagnosis onward
Prognosis & Follow-Up
Prognosis depends heavily on the stage at diagnosis — outcomes are considerably better when the cancer is localised to the skin than when lymph nodes are involved. Given the risk of recurrence, close follow-up is recommended in the years after treatment, with a low threshold for further imaging or biopsy if any new symptoms or lumps develop.