Polymorphous Low-Grade Adenocarcinoma Arising at the Retromolar Region：A Rare Case of High-Grade Malignancy

Polymorphous low-grade adenocarcinoma (PLGA) is an entity under the subclassification of adenocarcinoma from salivary glands. We report here a rare case of PLGA with suspected metastases to a regional lymph node and the liver, confirmed by magnetic resonance imaging and computed tomography. An 88-year-old Japanese woman complaining of pain in the left mandible, specifically in the gingiva upon swallowing, was referred to our clinical department in July 2003. The pain in the left mandibular gingiva had been noted 10 months before the first medical examination. Oral examination revealed a 38 x 30 mm mass forming from the left retromolar region to the glossopalatal arch with ulcer. An incisional biopsy of the mass revealed PLGA. Histopathologically, tumor cells presenting mild atypia showed tubular and cribriform structures. Immunohistochemically, the Ki-67 labeling index showed 31% suggesting a potential high-grade malignancy of tumor cells.