Frequent expression of glypican-3 in Merkel cell carcinoma: an immunohistochemical study of 55 cases.

The pathologic diagnosis of Merkel cell carcinoma (MCC) is mainly based on routine morphology and a characteristic cytokeratin 20 (CK20) immunohistochemical staining pattern. However, about 10% to 15% of MCCs are reportedly CK20 negative and about 10% to 20% of MCCs have only focal CK20 positivity.