Merkel cell carcinoma — SAQ

Stem

A 78-year-old man with a 40 pack-year smoking history presents with a 6-week history of a rapidly growing, painless, firm, red-violet nodule on the left temple. The lesion is 1.8 cm in diameter, dome-shaped, shiny, and non-tender. He had a renal transplant 10 years ago and takes tacrolimus and mycophenolate mofetil. He has no other systemic symptoms. Examination reveals a single lesion with no palpable cervical or parotid lymphadenopathy. You suspect Merkel cell carcinoma (MCC).

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Questions

a) What is the most likely diagnosis, and what clinical features support it? (2 marks)

^[2][3]b) Outline the investigations you would arrange to confirm the diagnosis and stage the disease. (3 marks)

c) Describe the definitive management of this patient assuming the lesion is localised and clinically node-negative. (3 marks)

d) What are the key prognostic factors and complications you would discuss with the patient? (2 marks)

Model answer

a) Diagnosis and supporting clinical features (2 marks)

^[2]- Most likely diagnosis: Merkel cell carcinoma (MCC), an aggressive primary cutaneous neuroendocrine carcinoma.

• Supporting features: AEIOU criteria — Asymptomatic/painless; Expanding rapidly (6 weeks); Immunosuppression (renal transplant on tacrolimus/mycophenolate); Older than 50 years (78 years); UV-exposed site (left temple). Additional features: firm, dome-shaped, red-violet, shiny nodule on sun-exposed skin of an elderly patient. Solid organ transplantation increases MCC risk approximately 10 to 24-fold.

^[1]b) Investigations (3 marks)

• Biopsy: punch or excisional biopsy of the lesion for histology and immunohistochemistry.
• Immunohistochemistry panel: CK20 with perinuclear punctate (dot-like) positivity (pathognomonic), neuroendocrine markers (chromogranin, synaptophysin, CD56, NSE), TTF-1 negative (distinguishes from SCLC), and MCPyV large T antigen (often positive).
• Staging: sentinel lymph node biopsy (SLNB) for clinically node-negative T1 or greater disease; baseline CT chest/abdomen/pelvis with contrast; consider 18F-FDG PET-CT for equivocal findings or high-risk primaries. Serum MCPyV antibody titres may be used as a baseline biomarker where available.

c) Definitive management (3 marks)

• Wide local excision (WLE) with 1 to 2 cm clinical margins down to deep fascia, or Mohs micrographic surgery if anatomical constraints (temple, head/neck) limit standard margins.^[2]
• Sentinel lymph node biopsy at the time of definitive excision using dual mapping (lymphoscintigraphy and blue dye or fluorescent tracer).
• Adjuvant radiotherapy to the primary site if margins are close/positive, lesion is larger than 1 cm, there is lymphovascular invasion, head/neck location, or immunosuppression. If SLNB is positive, nodal basin radiotherapy and/or completion therapeutic lymph node dissection.
• Multidisciplinary discussion involving dermatology, surgical oncology, radiation oncology, and medical oncology, especially given the transplant history and immunosuppression.

d) Prognostic factors and complications (2 marks)

• Prognostic factors: stage at presentation, tumour size, head/neck or trunk site, lymphovascular invasion, immunosuppression (transplant), positive SLNB, and MCPyV-negative status in some cohorts. Survival is stage-dependent — localised disease fares best and distant metastasis worst; recurrence is common and mostly early.^[2]
• Complications: local recurrence and in-transit/satellite metastases; regional nodal recurrence; distant metastases to lung, liver, bone, and brain; treatment complications including postoperative wound issues, radiotherapy skin toxicity, and immune-related adverse events if immunotherapy is required later. Paraneoplastic syndromes such as ectopic ACTH or hypercalcaemia are rare but recognised.

References4ShowHide

1. [1]Hernandez LE, Mohsin N, Yaghi M, et al. Merkel cell carcinoma: An updated review of pathogenesis, diagnosis, and treatment options Dermatol Ther, 2022.PMID 34967084
2. [2]Lugowska I, Becker JC, Ascierto PA, et al. Merkel-cell carcinoma: ESMO-EURACAN Clinical Practice Guideline for diagnosis, treatment and follow-up ESMO Open, 2024.PMID 38796285
3. [3]Lugowska I, Becker JC, Ascierto PA, et al. Merkel-cell carcinoma: ESMO-EURACAN Clinical Practice Guideline for diagnosis, treatment and follow-up ESMO Open, 2024.PMID 38796285
4. [4]Strong J, Hallaert P, Brownell I. Merkel Cell Carcinoma Hematol Oncol Clin North Am, 2024.PMID 39060119