Glycogen-rich adenocarcinoma in the lower lip: report of a case with particular emphasis on differential diagnosis

We herein report a glycogen-rich adenocarcinoma occurring in the lower lip of a 44-year-old female. The lesion appeared as painless slowly growing mass in the right side of the lower lip. Histologically, infiltrative tumor nests with duct-like or pseudocyst structure into the mucosa and/or dermis were observed. The basaloid neoplastic cells had granular but occasionally vacuolated cytoplasm with salient reaction of diastase-digestible periodic acid-Schiff, thus indicating that they were glycogen-rich in nature. The tumor cells were positive for CEA, cytokeratin, and S-100 protein, and negative for SMA, alpha-1 antitrypsin, and amylase by immunohistochemistry. The origin of the tumor with infiltrative nests was indistinguishable from salivary gland and skin appendage malignancy. A differential diagnosis of this peculiar neoplasm was discussed.