Abstract
Squamous cell carcinoma of the head and neck, particularly basaloid squamous cell carcinoma, may be difficult to distinguish from high-grade adenoid cystic carcinoma. Evidence of human papilloma virus (HPV) infection, particularly HPV 16, is frequently found in non-keratinizing oropharyngeal squamous cell carcinoma. Immunoreactivity for p16, a surrogate marker for HPV infection, often parallels the HPV infection status in oropharyngeal squamous cell carcinoma. However, the incidence and correlation between p16 expression and HPV infection in high-grade adenoid cystic carcinoma is unknown. Sixteen cases of high-grade adenoid cystic carcinoma, three cases of dedifferentiated adenoid cystic carcinoma and eight cases of low-/intermediate-grade adenoid cystic carcinoma were identified for inclusion in the study. All cases were tested by immunohistochemistry for p16 expression and in situ hybridization for high- and low-risk HPV. Eight cases (100%) of low-to-intermediate-grade adenoid cystic carcinoma were focally positive for p16, all of which were negative for HPV. In all, 14 of 16 cases (88%) of high-grade adenoid cystic carcinoma and three cases (100%) of dedifferentiated adenoid cystic carcinoma were positive for p16; strong and diffuse staining was noted in three cases (3 of 19, 16%). Two cases (11%) of high-grade adenoid cystic carcinoma, which were also diffusely positive for p16, showed the presence of high-risk HPV. These findings suggest that the presence of HPV infection in high-grade adenoid cystic carcinoma is infrequent, even in the presence of p16 immunostaining. Nevertheless, HPV positivity should not be used to exclude the possibility of high-grade adenoid cystic carcinoma when the differential diagnosis includes squamous cell carcinoma. Moreover, although p16 overexpression is often used as a surrogate marker for HPV in squamous cell carcinoma, it cannot be used in this manner in high-grade adenoid cystic carcinoma.
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