Basal cell carcinomas of the vulva: high-risk human papillomavirus DNA detection, p16 and BerEP4 expression.

Basal cell carcinoma (BCC) of the vulva is rare and may be confused with the much more commonly encountered high-risk human papillomavirus (HPV)-related basaloid squamous cell carcinoma (SCC). The HPV status of BCCs is not well established. This study assesses the utility of p16 and BerEP4 expression patterns and high-risk HPV detection for distinction of these tumors. Thirteen cases of vulvar BCC were analyzed by immunohistochemistry for p16 and BerEP4 expression. HPV status was assessed by in situ hybridization (ISH) with a high-risk HPV wide-spectrum probe and HPV 16 and 18 type-specific probes. All tumors (13/13) demonstrated patchy p16 positivity, with <50% of tumor cells expressing p16 in all cases. None demonstrated the diffuse p16 expression characteristic of high-risk HPV-associated lesions. No high-risk HPV was detected by ISH (0/13). Eleven of 13 (85%) vulvar BCCs showed diffuse, intense expression of BerEP4. The 2 BerEP4-negative cases were notably squamatized. The lack of diffuse p16 expression and failure to detect high-risk HPV by ISH in vulvar BCCs indicate that these tumors are unrelated to high-risk HPV. Thus, these ancillary techniques, particularly p16 immunohistochemistry, are useful for distinguishing vulvar BCCs from basaloid forms of high-risk HPV-related vulvar SCC. BerEP4 expression can help in distinction of these tumors except in cases of BCC with extensive squamatization. Distinction of vulvar BCC from basaloid SCC is important because of differences in extent of surgical treatment for these entities.