Lymph nodal Merkel cell carcinoma: primary tumor or metastasis from unknown primary site?

摘要

Merkel cell carcinoma represents rare, aggressive skin cancer with neuroendocrine differentiation. Most Merkel cell carcinomas develop within the skin of the head and neck or on the extremities; in <10% of cases, the trunk or mucus membranes are involved. Regional lymph node metastases occur in 50-66% of cases.In 1992, Eusebi et al. described eight cases of nodal Merkel cell carcinoma in the absence of an identifiable primary malignancy. Since that time, other authors ' have reported cases of 'primary' nodal Merkel cell carcinoma and have raised the issue of whether this phenomenon truly occurs or whether such nodal involvement represents, instead, metastasis from an occult tumor. In such cases, strict criteria should be applied before rendering a diagnosis of primary nodal Merkel cell carcinoma. In addition, there is need for specific immunohisto-chemical evidence to support the diagnosis.