Primary Cutaneous Adenoid Cystic Carcinoma of the Scalp With p16 Expression: A Case Report and Review of the Literature

Introduction:Adenoid cystic carcinoma (ACC) is a rare carcinoma that typically arises in salivary glands but can also occur in other sites including skin. Primary salivary ACC is a locally aggressive tumor characterized by local recurrence and late metastasis. Primary cutaneous ACC is found predominately on the scalp and is more indolent than salivary ACC; and, despite a high incidence of local recurrence, metastases are exceedingly rare. Methods:A 62-year-old white male presented with a 6-mm mobile, blue-tinted nodule on the left mid scalp unchanged for several years. Results:The histopathological findings of an excisional biopsy were diagnostic for a primary cutaneous ACC. Immunohistochemistry demonstrated focal positivity for p16. Conclusions:Primary cutaneous ACC is a rare malignancy that should be considered in the differential diagnosis of adnexal neoplasms and, when occurring on the head and neck, must be distinguished from cutaneous involvement by salivary ACC. The majority of reported salivary ACC with p16 protein expression were not positive for high-risk human papilloma virus by in situ hybridization. Immunostaining for p16 has previously been reported in salivary gland ACC. This is the first report in the English literature of p16 immunoexpression in primary cutaneous ACC.