Merkel Cell Carcinoma (MCC)

MCC:
- Also known as primary small-cell carcinoma of the skin and anaplastic carcinoma of the skin:
  - Is a rare, aggressive cutaneous malignancy
Risk factors for MCC include:
- Immunosuppression:
  - Human immunodeficiency virus (HIV) infection
  - Cancer
  - Organ transplant
- Chemotherapy
- Radiation
- Arsenic
- Sun exposure
Approximately 80% of Merkel cell tumors:
- Harbor a polyoma virus:
  - But its role in pathogenesis remains unclear
The cornerstone of management for MCC is:
- Wide local excision with a margin of 1 to 2 cm
- Nodal staging in clinically node-negative patients:
  - Is a subject of controversy:
    - About one third of the patients with MCC will have a positive SLN:
      - SLN biopsy does not appear to have an impact on survival but does improve local control
    - On the basis of the current evidence, National Comprehensive Cancer Network guidelines:
      - Recommend routine SLN biopsy for clinically node-negative MCC
MCC is an extremely radiosensitive tumor:
- A recent randomized study for stage 1 Merkel cell carcinoma:
  - Showed significant reduction on regional recurrence with radiation
- A retrospective Surveillance, Epidemiology, and End Results (SEER) database study:
  - Demonstrated an improvement in survival for patients who received adjuvant radiation:
    - This effect was more pronounced in the 2 cm tumors
  - Recommendations for adjuvant radiation after appropriate surgical resection are still unclear:
    - However, adjuvant radiation therapy to the primary tumor site should be considered for:
      - Larger ( greater than 1 cm) tumors with adverse features such as:
        
        Perineural invasion and lymphovascular invasion
    - In high-risk cases that omit a SLN biopsy:
      - Radiation to nodal basin is recommended
  - Regional lymph node dissection and / or nodal irradiation is recommended for patients with nodal metastases;
    - However, for resectable lesions there is no role for neoadjuvant radiation therapy
References:
- Gupta SG, Wang LC, Peñas PF, Gellenthin M, Lee SJ, Nghiem P. Sentinel lymph node biopsy for evaluation and treatment of patients with Merkel cell carcinoma: The Dana-Farber experience and meta-analysis of the literature. Arch Dermatol. 2006;142:685-690.
- Jouary T, Leyral C, Dreno B, et al. Adjuvant prophylactic regional radiotherapy versus observation in stage I Merkel cell carcinoma: A multicentric prospective randomized study. Ann Oncol. 2012;23:1074-1080.
- Mehrany K, Otley CC, Weenig RH, Phillips PK, Roenigk RK, Nguyen TH. A meta-analysis of the prognostic significance of sentinel lymph node status in Merkel cell carcinoma. Dermatol Surg. 2002; 28:113-117.Mojica P, Smith D, Ellenhorn JD. Adjuvant radiation therapy is associated with improved survival in Merkel cell carcinoma of the skin. J Clin Oncol. 2007;25:1043-1047.