Merkel cell carcinoma

We read with interest the article by Gollard et al.,1 who reviewed their experience with Merkel cell carcinoma (MCC). Although we believe the authors did excellent work in their clinicopathologic studies, we would like to point out a major hallmark of MCCs that was not mentioned by the authors. Patients with small cell neuroendocrine carcinoma may present with metastasis to the skin even before the primary lesion is detected; thus it is important to distinguish these latter tumors from primary MCC for obvious treatment decisions. Because both entities are indistinguishable based on routine histologic examination, the use of cytokeratin 20 antibodies via immunohistochemical techniques is extremely helpful in establishing the diagnosis of MCC because this marker is extremely sensitive and very specific for the detection of MCC.2-7 Therefore, as demonstrated by Chan et al.,8 positivity for cytokeratin 20 in a small cell carcinoma of uncertain origin is a strong predictor of MCC. Hadi Yaziji M.D.*, Allen M. Gown M.D.*, * PhenoPath Laboratories and, Immunocytochemistry Institute of Seattle, Seattle, Washington