Cutaneous neuroendocrine (Merkel cell) carcinoma occurred after resection of malignant melanoma

An elderly man presented with a brown border nodule of the left upper lip that appeared to be clinically consistent with metastatic melanoma; he had previously undergone two surgical removals of melanoma in the right temporal region. Routine histologic examination was not sufficient for diagnosis, but Merkel cell carcinoma was diagnosed by immunohistochemical studies Neuroendocrine carcinoma of viscera was excluded. Because this case could not be differentiated from amelanotic melanoma and malignant lymphoma based on histologic appearances, immunohistochemical staining was helpful for diagnosis and differentiation.