Merkel cell carcinoma (MCC) is a rare aggressive skin cancer with neuroendocrine differentiation. With immunohistochemistry, the tumor cells stain for both neuroendocrine (i.e., synaptophysin and chromogranin A) and epithelial markers. The epithelial marker cytokeratin 20 (CK20) stains positive with immunohistochemistry in a vast majority of MCCs. The expression of the special AT-rich sequence-binding protein (SATB2) was analyzed in MCC (n = 20) together with other forms of skin cancer and neuroendocrine tumors (n = 51) using immunohistochemistry. The results were compared to the expression of CK20, synaptophysin, and chromogranin A. The majority of the MCCs stained positive for synaptophysin and chromogranin A (95 vs 80 % respectively), and 75 % of the MCCs showed cytoplasmic positivity for CK20 and nuclear positivity for SATB2, with two discordant cases lacking expression of one of these markers. We conclude that immunohistochemistry for SATB2 can be used as an additional marker with similar sensitivity and specificity as CK20 for the diagnosis of Merkel cell carcinoma, suggesting a clinical utility in difficult cases where MCC is suspected.
Keywords: CK20; Immunohistochemistry; Merkel cell carcinoma; SATB2; Tissue microarray.