Abstract:

Hypothesis: Basal cell carcinoma (BCC) is one of the most common diagnoses encountered in dermatopathology. While most BCCs are readily diagnosed based on histopathologic features, some may present a diagnostic challenge, especially when exhibiting uncommon cytomorphologic characteristics. Herein, we examine clear-cell BCC, a variant which may mimic trichilemmoma, especially in small, superficial or fragmented biopsy specimens. Criteria to effectively distinguish these two entities have not been investigated previously. We propose the use of Ber-EP4 and CD34 immunohistochemical (IHC) stains to distinguish these two clear-cell neoplasms. Methods: Formalin fixed paraffin embedded sections from clear-cell BCC (n=5) and trichilemmomas (n=7) were stained with hematoxylin and eosin, Ber-Ep4, and CD34. The findings were analyzed by both authors, including a board-certified dermatopathologist (JMS). Results and Conclusion: IHC staining with Ber-EP4, a commonly used marker of follicular germinative differentiation, is preserved in all cases of clear-cell BCC, whereas CD34, which labels trichilemmoma in a membranous fashion, is absent in 4/5 cases and expressed in only limited fashion in 1/5 cases. In contrast, all cases of trichilemmoma show membranous staining with CD-34 and are negative for Ber-EP4 expression. Thus, differential expression of Ber-EP4 and CD34 can be a useful tool to distinguish between clear-cell BCC and trichilemmoma in challenging situations.

Financial Disclosure:
No current or relevant financial relationships exist.

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Anupam Mitra, MBBS, MD