Immunohistochemical characterization of the differentiation state of basal cell carcinomas with special interest for infiltrating relapsing tumors.

A retrospective histological and immunohistochemical study was performed on 66 basal cell carcinomas (BCC). To determine the differentiation stages of epithelial cells in these BCC, three monoclonal antibodies directed against cytokeratins K1, K2, K9 and K10-11 (EE21-06), to cytokeratins K1 to K19 (F12-19), and to corneodesmosin (G36-19) were used in indirect immunofluorescence on paraffin-embedded sections. Three histological groups of BCC with specific cytokeratin immunohistochemical features were distinguished: (1) superficial BCC were unlabelled, (2) nodular and variant (keratotic, adenoid) BCC showed an homogeneous labelling, and (3) infiltrative aggressive-type BCC showed a heterogeneous cell to cell labelling. Some nodular BCC cells presented characteristics of granular keratinocytes, i.e. they were labelled by the anticorneodesmosin antibody. All the clinically recurrent tumors were found to be of the infiltrative aggressive-type. If these aggressive forms of BCC were not identified by specific marker, their topographic patterns of labeling with antibodies directed to cytokeratins allowed them to be distinguished. We suggest that an immunohistochemical analysis with antibodies specific for different stages of keratinocyte differentiation is an efficient complement to histological diagnosis of BCC.