Merkel Cell Carcinoma
Also known as: MCC
Rare but highly aggressive. Appears as a painless, fast-growing, firm nodule - often flesh-colored or bluish-red.
What to look for
Side-by-side comparison
Normal skin
No firm lumps
Possible MCC
Firm, painless, fast-growing
Merkel cell carcinoma is a rare and aggressive neuroendocrine skin cancer that develops in Merkel cells, which are sensory cells located near nerve endings in the skin. It is approximately 40 times rarer than melanoma but has a higher mortality rate stage-for-stage.
MCC typically presents as a rapidly growing, firm, painless, dome-shaped nodule on sun-exposed skin - most commonly the head, neck, or arms. The tumor is often flesh-colored, pink, red, or bluish-purple. Because it looks benign and does not cause pain, it is frequently misdiagnosed as a cyst, pimple, or insect bite.
The acronym AEIOU helps identify suspicious features: Asymptomatic (painless), Expanding rapidly, Immunosuppressed patient, Older than 50, UV-exposed site. A nodule meeting three or more of these criteria should raise strong suspicion for MCC.
About 80% of MCCs are associated with the Merkel cell polyomavirus (MCPyV). The virus is common and usually harmless, but in rare cases can trigger uncontrolled cell growth. Immunosuppression is a major risk factor - transplant recipients have a 10-fold increased risk.
Quick self-check
Does this look like merkel cell carcinoma? Answer 2 questions.
Is the nodule firm, dome-shaped, and painless?
Has it grown rapidly (weeks rather than months)?
Risk factors
- Age over 50 (median age at diagnosis is 76)
- Chronic sun exposure on fair skin
- Weakened immune system (transplant, HIV, chronic lymphocytic leukemia)
- Merkel cell polyomavirus (MCPyV) infection
- History of other skin cancers
When to see a dermatologist
- ⚠A rapidly growing, painless, firm nodule on sun-exposed skin
- ⚠A new skin lump that is flesh-colored, pink, or bluish-red
- ⚠Any fast-growing lump in an immunosuppressed person over 50
Often confused with
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Full ABCDE check →Frequently asked questions
How rare is Merkel cell carcinoma?
About 3,000 cases are diagnosed annually in the US, compared to approximately 100,000 melanomas. However, MCC has a higher mortality rate stage-for-stage than melanoma, making early detection especially critical.
What does the AEIOU acronym mean for MCC?
A = Asymptomatic (painless), E = Expanding rapidly, I = Immunosuppressed, O = Older than 50, U = UV-exposed site. If a skin nodule matches three or more of these criteria, MCC should be considered and a biopsy performed.