In the present study, to identify the clinical significance of the cytokeratin (CK) 20 staining pattern in Merkel cell carcinoma (MCC), we retrospectively analyzed the major clinicopathological and immunohistochemical characteristics of 12 cases of MCC. Typical dot-like pattern was seen in eight of our patients, while four patients showed peripheral staining pattern. Interestingly, all cases of MCC with dot-like CK20 tumor cells occurred in the head and neck region, while those with peripheral CK20 pattern tended to be located in other lesions (forearm, knee, or buttock): The difference of frequency in the head and neck regions was statistically significant. Dot-like CK20 staining pattern may therefore be resulted from ultraviolet exposure. Additionally, although without significance, metastasis was more frequent in those with dot-like CK20 than in peripheral CK20 staining: All patients with peripheral CK20 pattern had complete remission by surgical excision with or without radiation therapy. CK20 staining pattern may be a novel predictor of prognosis.
Keywords: CK20; Immunohistochemistry; skin.