The immunohistochemical characteristics of the basosquamous cell carcinoma

BACKGROUND. The basosquamous cell carcinoma (BSCC) is a poorly defined and often misunderstood cutaneous malignancy. OBJECTIVE. The purpose of this study was to compare, using immunohistochemical techniques, the BSCC, basal cell carcinoma (BCC), and squamous cell carcinoma (SCC). METHODS. BSCC occurring at Pennsylvania State University over the past 10 years were identified. Choosing seven BCC, and nine SCC as controls, all specimens were stained for keratin, lack of apoptosis, glycoproteins, and altered gene products using the avidin/biotin and strep-avidin immunoperoxidase techniques. Each malignancy was then graded for the percentage of cells stained with each marker. RESULTS. Of the markers studied, all stained to varying degrees the malignant aspects of the specimens. There were similar patterns between tumors, with the BSCC showing a transition zone between typical BCC and SCC. This was most striking for Ber-EP4, where over two- thirds of the BCC stained, none of the SCC, and half of the BSCC showed reactivity. CONCLUSION. BSCC has staining patterns similar to both the BCC and SCC. The presence of a transition zone does not support the concept that all BSCC are collision tumors, but rather a differentiation of one tumor into another. We confirm earlier reports that Ber-EP4 could be used to distinguish between classic BCC and SCC. AE1/AE3, bcl-2, TGF-alpha, and p53 were not helpful in separating the tumors.