Abstract
Pleomorphic adenoma (PA), the most common salivary gland tumor, accounts for 54 to 65% of all salivary gland neoplasias and 80% of the benign salivary gland tumors. It most frequently affects the parotid gland, followed by the submandibular and the minor salivary glands. Microscopically, mucous, sebaceous, oncocytic and squamous metaplasia, sometimes with the formation of keratin pearls, may be present, but the latter rarely results in the formation of extensive keratin-filled cysts lined by squamous epithelium. Extensive squamous metaplasia can be mistaken for malignancy, including mucoepidermoid carcinoma and squamous cell carcinoma. Here, we present an unusual case of PA with extensive squamous metaplasia and keratin cyst formations in a minor salivary gland, and discuss its microscopic features, including the immunohistochemical characteristics, and differential diagnosis of this uncommon presentation.
Highlights
Pleomorphic adenoma (PA) affecting minor salivary glands presents a female predilection29
We present an unusual case of PA with extensive squamous metaplasia and keratin cyst formations in a minor salivary gland
The cases of PA presenting extensive NHUDWLQ¿OOHG F\VWV OLQHG E\ VTXDPRXV HSLWKHOLXP are referred to in the literature as “cystic PA with extensive adnexa-like differentiation”, since the histologic features mimic cutaneous appendages7,25
Summary
Pleomorphic adenoma (PA) affecting minor salivary glands presents a female predilection. We present an unusual case of PA with extensive squamous metaplasia and keratin cyst formations in a minor salivary gland. Tumoral epithelial cells formed solid sheets, nests, cords and ductal structures, the latter presenting a lumina lined by a double layer of cells and frequently containing eosinophilic material (Figures 2D and 2E), which rarely presented small IRFL RI FDOFL¿FDWLRQ 3$6 UHDFWLRQV DQG $OFLDQ EOXH staining revealed the presence of mucin inside the ductal structures. Nests and cords presented immunopositivity that was either focal for CK7, CK19, vimentin, GFAP and S-100, or frequent for high-molecular-weight CKs. Cells in the basal layer of the epithelial cords were positive for p63. The proliferative index of the lesion, expressed as the percentage of Ki-67-positive neoplastic cells among the total number of cells FRXQWHG LQ UDQGRPO\ VHOHFWHG ¿HOGV ZDV ORZ (2.63%) and proliferation was mainly localized in the outer layers of the epithelial lining of the large keratin cysts. The postoperative course was uneventful and the patient has been reviewed regularly, with no evidence of recurrence 3 years after excision
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