| Clear cell squamous cell carcinoma in situ (clear cell SCCIS) has not been defined in the literature. The goals of this thesis is first, to review the literature on clear cell lesions of the skin and discuss the importance of the differential diagnosis; second, to characterize the clinical and histological features of clear cell squamous cell carcinoma in situ, and third, to define the special histochemical and immunohistochemical features of clear cell SCCIS to elucidate the type of cell differentiation and help distinguish it from other clear cell neoplasms of the skin. Clear cell SCCIS must be distinguished from other clear cell neoplasms of the skin to avoid misdiagnosis and increased burden of patient and physician time and medical expenses. Eighty-one cases of SCCIS with ≥5% clear cell change were identified among 1497 cases of SCCIS over an 18 month period and represented 5.5% of all SCCIS. Clear cell SCCIS was defined as having ≥95% clear cell change. It represented only 0.15% of SCCIS. The clinical features of all SCCIS with clear cell change, including age, sex and site distribution did not vary significantly from typical SCCIS using chi square analysis. Periodic acid-Schiff special staining and immunohistochemical analysis indicated that the clear cells in clear cell SCCIS differentiate toward outer root sheath cells. Antibodies most useful in labeling outer root sheath cells and SCCIS with clear cell changes were K 8.12 (labeling CK 13 and CK 16) in 100% of cases, cellular retinoic acid binding protein II (CRABP II) in 83% of cases, CAM 5.2 in 58% of cases and CK15 in 50% of cases. This study defines clear cell SCCIS on the end of the spectrum of SCCIS with clear cell change and this spectrum displays ORS differentiation. |
