Anti‐cytokeratin 20 staining of Merkel cells helps differentiate basaloid proliferations overlying dermatofibromas from basal cell carcinoma

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Abstract
Basaloid epidermal proliferations (BEP), morphologically resembling basal cell carcinoma (BCC), have been described overlying dermatofibromas. Distinguishing the two is important because of non-aggressiveness of BEP and local aggressiveness of BCC. The aim of this study is to determine whether CK20 antibody staining for Merkel cells can be used as an adjunct method to differentiate BEP from BCC. Ten cases of BEP overlying dermatofibromas were selected. Ten cases of BCC were used as control. The two groups were stained with CK20 antibody. Numerical density of CK20 stained Merkel cells in peri-lesional epidermis, BEP and BCC was determined by examining 300 cells at 400X in two separate areas by three independent pathologists. To determine statistical significance, the results were compared using t-test method. Density of Merkel cells in peri-lesional epidermis was 0.2-0.3%. No merkel cells were detected in the BCC. BEP overlying dermatofibromas showed an obvious increase in CK 20 stained Merkel cells. The difference was statistically significant (P < 0.02) CONCLUSIONS: We report a significant increase in CK20 stained Merkel cells in BEP overlying dermatofibromas as compared to BCC. CK20 antibody staining for Merkel cells can be used as an adjunct method to differentiate BEP overlying dermatofibromas from BCC. Mahmoodi M, Asad H, Salim S, Kantor G, Minimo C. Anti-CK20 staining of Merkel cells helps differentiate basaloid proliferations overlying dermatofibromas from basal cell carcinoma.