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Merkel cell carcinoma — Clinical Guidelines

Overview

Merkel cell carcinoma (MCC) is a rare, highly aggressive neuroendocrine skin cancer characterized by high recurrence and metastatic potential. It predominantly affects older adults, particularly those with immunosuppression or UV exposure, and has seen an increasing incidence 1 3.

Diagnosis

Clinical Presentation: Typically presents as a rapidly growing, painless nodule, often in sun-exposed areas 1 3.

Histopathology: Characterized by small, blue cells with high nuclear-to-cytoplasmic ratio, positive for cytokeratin 20 and often associated with Merkel cell polyomavirus (MCPyV) 1 3 5.

Immunostaining: CK20 positivity and MCPyV status are crucial for diagnosis 5.

Staging: Utilize imaging (CT, MRI, PET) and sentinel lymph node biopsy for accurate staging 2 3.

Pathology Reporting: Adhere to standardized datasets for comprehensive pathology reports 4.

Management

Localized Disease: Surgical resection with clear margins is recommended 2 3.

Adjuvant Therapy: Consider adjuvant radiotherapy for high-risk features 2 3.

Metastatic/Advanced Disease: Immune checkpoint inhibitors (e.g., pembrolizumab) are first-line treatments 2 6.

RB1 Mutations: Consider as a prognostic factor and guide treatment decisions 5.

Multidisciplinary Approach: Management should involve a multidisciplinary team with expertise in oncology and dermatology 2 3.

Special Populations

Immunocompromised Patients: Higher risk and may require more aggressive monitoring and treatment 1 3.

Elderly: Often affected; treatment should consider comorbidities and functional status 1 3.

Key Recommendations

Surgical Resection: For localized MCC, perform complete surgical resection with clear margins 2 3 (Evidence: Strong).

Immune Checkpoint Inhibitors: Use pembrolizumab for metastatic or advanced MCC 2 6 (Evidence: Moderate).

Multidisciplinary Care: Implement management strategies within a multidisciplinary team 2 3 (Evidence: Expert opinion).

Pathology Reporting Standards: Adopt internationally agreed-upon datasets for pathology reports 4 (Evidence: Expert opinion).

References

1 Nakamura M, Nagase K, Kato J, Yasuda M, Tomita N, Kobayashi T et al.. Japanese Dermatological Association Guidelines: Clinical Questions of Guidelines for Merkel Cell Carcinoma 2025. The Journal of dermatology 2025. link 2 Lugowska I, Becker JC, Ascierto PA, Veness M, Blom A, Lebbe C et al.. Merkel-cell carcinoma: ESMO-EURACAN Clinical Practice Guideline for diagnosis, treatment and follow-up. ESMO open 2024. link 3 Gauci ML, Aristei C, Becker JC, Blom A, Bataille V, Dreno B et al.. Diagnosis and treatment of Merkel cell carcinoma: European consensus-based interdisciplinary guideline - Update 2022. European journal of cancer (Oxford, England : 1990) 2022. link 4 Busam KJ, Judge MJ, Bichakjian CK, Coit D, Kutzner H, Requena L et al.. Dataset for the Reporting of Merkel Cell Carcinoma: Recommendations From the International Collaboration on Cancer Reporting (ICCR). The American journal of surgical pathology 2022. link 5 Muto Y, Ryo E, Namikawa K, Takahashi A, Ogata D, Fujimura T et al.. RB1 gene mutations are a distinct predictive factor in Merkel cell carcinoma. Pathology international 2021. link 6 Sherry AD, Bezzerides M, Khattab MH, Luo G, Ancell KK, Kirschner AN. An autoimmune-based, paraneoplastic neurologic syndrome following checkpoint inhibition and concurrent radiotherapy for merkel cell carcinoma: case report. Strahlentherapie und Onkologie : Organ der Deutschen Rontgengesellschaft ... [et al] 2020. link 7 Vázquez Doval J, Llombart Cussac B, Pérez Bustillo A, Paradela de la Morena S, Fuente González MJ, Fernández Figueras MT et al.. Diagnosis and Treatment of Merkel Cell Carcinoma in Specialized Dermatology Units: A Clinical Practice Guideline of the Spanish Academy of Dermatology and Venereology. Actas dermo-sifiliograficas 2019. link 8 Fan T, Song YJ, Liu XL, Zhou J, Yang H, Wei YN et al.. Primary Merkel Cell Carcinoma on the Cheek: Three Case Reports. Journal of the College of Physicians and Surgeons--Pakistan : JCPSP 2017. link 9 Lebbe C, Becker JC, Grob JJ, Malvehy J, Del Marmol V, Pehamberger H et al.. Diagnosis and treatment of Merkel Cell Carcinoma. European consensus-based interdisciplinary guideline. European journal of cancer (Oxford, England : 1990) 2015. link 10 Ness KH, Morton TH, Dale BA. Identification of Merkel cells in oral epithelium using antikeratin and antineuroendocrine monoclonal antibodies. Journal of dental research 1987. link 11 Hartschuh W, Weihe E, Büchler M, Helmstaedter V, Feurle GE, Forssmann WG. Met enkephalin-like immunoreactivity in Merkel cells. Cell and tissue research 1979. link

Merkel cell carcinoma