Cutaneous clear cell squamous cell carcinoma in situ :: clinical, histological and immunohistochemical characterization

Background: Clear cell squamous cell carcinoma in situ (SCCIS) has not been defined in the literature with respect to its clinical, histological, and immunohistochemical features. Methods: Nearly 1500 consecutive cases of SCCIS were assessed for percent clear cell change. The clinical features of all SCCIS with >= 10% clear cell change, including age, sex and site distribution, were compared with classical SCCIS using chi-square analysis. PAS special staining and immunohistochemical analysis with 11 cell markers were performed to characterize the clear cell of origin. Results: Eighty SCCIS cases with a spectrum of clear cell change of >= 10% were identified. Six cases with >= 80% clear cells were defined as clear cell SCCIS. The clinical features of the cases did not vary significantly from classical SCCIS. Antibodies labeling outer root sheath (ORS) cells also labeled clear cells in the cases and included K8.12 (labeling CK13 and CK16), cellular retinoic acid binding protein II, CAM 5.2 and CK15. Antibodies that did not label ORS cells, but did label eccrine glands (CK7 and CK18) or sebocytes (EMA), also did not label the cases. Conclusion: Clear cell change in SCCIS is part of a spectrum which displays ORS differentiation.