What is a characteristic of Merkel cell carcinoma (MCC)?

Merkel Cell Carcinoma: Key Characteristics

Merkel cell carcinoma (MCC) is highly radiosensitive, making radiation therapy an important component in its management that can significantly improve prognosis and survival outcomes. 1

Epidemiology and General Characteristics

• MCC is a rare, aggressive cutaneous neuroendocrine tumor with high mortality rates exceeding those of melanoma, with 5-year survival rates ranging from 30% to 64% 2
• MCC predominantly affects elderly Caucasians (≥65 years) and typically occurs on sun-exposed skin areas, particularly the head and neck 2
• Immunosuppressed individuals, including those with organ transplants, lymphoproliferative malignancies, or HIV infections, have a disproportionately higher risk of developing MCC 2, 3

Metastatic Patterns and Prognosis

• MCC has a high propensity for regional lymph node metastasis, with 52-59% of cases developing regional disease, contradicting option (c) which incorrectly states it "seldom spreads to regional lymph nodes" 2
• Several large reviews document distant metastatic disease in 34-36% of all MCC cases 2
• MCC has higher local recurrence rates (25-30% of cases) compared to melanoma, refuting option (d) which incorrectly states it is "less likely than melanoma to recur after local excision" 2
• Location on the trunk does not confer the best prognosis as suggested in option (b); in fact, MCC tends to occur most commonly on sun-exposed areas like the head and neck (29-48% of all primary MCCs) 2

Pathophysiology and Diagnosis

• Merkel cell polyomavirus (MCPyV) is detected in 43-100% of MCC tumor samples and plays a significant role in pathogenesis 2
• Diagnosis requires immunohistochemical staining, typically with cytokeratin 20 (CK-20) and thyroid transcription factor-1 (TTF-1) to differentiate from small cell lung cancer 2

Treatment Considerations

• Surgery is the mainstay of treatment for localized disease, but radiation therapy plays a crucial role in management 4, 1
• MCC is highly radiosensitive, and adjuvant radiotherapy can increase 5-year survival rates from 30-40% after surgery alone to approximately 75% 1
• The integration of radiotherapy into the therapeutic approach significantly improves prognosis, highlighting the tumor's radiosensitivity 1
• For advanced disease, immune checkpoint inhibitors have demonstrated durable antitumor activity 5, 6

Common Pitfalls in MCC Management

• Delayed diagnosis is common due to MCC's innocuous appearance, often leading to diagnosis at advanced stages 6
• Relying solely on surgical excision without adjuvant radiotherapy may result in suboptimal outcomes given MCC's high radiosensitivity 1
• Failure to perform sentinel lymph node biopsy may miss regional metastases, which occur frequently in MCC 2

Based on the evidence provided, option (a) - MCC is highly radiosensitive - is the correct characteristic of Merkel cell carcinoma, as supported by clinical evidence showing significant improvement in survival rates with the addition of radiotherapy.