Cutaneous neuroendocrine carcinoma

Definition

Cutaneous neuroendocrine carcinoma is a primary cutaneous cancer arising from a subset of skin neuroendocrine cells (Merkel cells, giving the name Merkel cell carcinoma (MCC)). MCC is rare accounting for less than 1% of all cutaneous malignancies. The estimated annual incidence ranges from 1 to 2 per 500,000 in the white population, but figures are steadily increasing. MCC generally occurs in older white adults (mean age at diagnosis 68-75 years), only 5% of cases occur before the age of 50 years. There is no major sex predilection, although some authors report a slight male predominance. MCC usually appears as firm, painless, shiny lumps of skin (red, pink, or violet lumps of various sizes). It usually develops in sun-exposed areas (head, neck, and arms). MCC is fast-growing: it tends to spread quickly to the regional lymph nodes and then metastasizes to other organs, in particular the liver, bone, lungs, and brain. At the time of diagnosis, MCCs are generally characterized by a primary lesion, growing in the dermis and subcutaneous tissues, with or without lymph node metastases. MCC is divided into stages depending on the extent of disease. The exact cause of MCC is unknown, but it appears to be linked to sun exposure and immunosuppression. The diagnosis of MCC is based on a skin biopsy. Histologically, MCCs are poorly differentiated neuroendocrine carcinomas involving the dermis and frequently extending to the subcutaneous tissue. Immunohistochemistry reveals positivity for neuroendocrine (neuron-specific enolase, synaptophysin) and cytokeratin markers (cytokeratin 20), allowing MCC to be differentiated from other small cell tumors. Imaging methods are used to investigate the presence of metastases in other organs. Management depends on the stage of the tumor at diagnosis, tumor size and location, and the age and general health status of the patient. Treatment includes surgery (wide local excision and selective lymphadenectomy), radiation therapy and chemotherapy (only for patients with metastatic disease). Supportive care should be offered to improve the quality of life of patients. Most deaths from MCC occur within the first 3 years after diagnosis. Patients with no lymph node disease, however, may have an excellent prognosis. Women appear to have a better survival rate than men.

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