Pleomorphic adenoma with extensive adenoid cystic carcinoma‐like cribriform areas of parotid gland

We report an interesting case of pleomorphic adenoma (PA) with extensive adenoid cystic carcinoma (ACC)-like cribriform areas of parotid gland along with a discussion of the differential diagnosis. The patient was a 62-year-old-female who presented with a 5-month history of a slow-growing painless mass in the left preauricular region. Pathological examination of the excised mass revealed a well-encapsulated tumor consisting of typical PA areas and extensive ACC-like cribriform areas. The transition between both areas was frequently observed. There was no clinical or histological evidence of a longstanding PA, such as prominent hyalinization with dystrophic calcification. Immunohistochemically, the neoplastic myoepithelial cells of the PA areas showed frequent expression of vimentin and S-100 protein, along with occasional positivity for glial fibrillary acidic protein and alpha-smooth muscle actin. The immunoreactivity of the neoplastic myoepithelial/basal cells forming cribriform nests was essentially identical to that of the PA areas. The difference of immunoreactivity of the basal/myoepithelial cells between PA and ACC may have some discriminatory advantage. In addition, the low proliferative activity observed in the entire tumor suggested that the cribriform nests resembling ACC are also the component of PA.