The importance of postoperative radiotherapy against polymorphous low-grade adenocarcinoma of the parotid gland: case report and review of the literature.

Polymorphous low-grade adenocarcinoma (PLGA) of the salivary gland is a disease entity that is a recently described form of adenocarcinoma. PLGA most commonly arises in the minor salivary glands. We report two cases of PLGA of the parotid gland. Case 1: A 52-year-old female visited the University of Tsukuba Hospital with a painless mass in the left parotid region. A superficial parotidectomy and postoperative radiotherapy were performed. The patient has been free from disease for 50 months. Case 2: A 55-year-old female initially noticed a painless slowly growing mass in the left parotid region. The tumor was removed with a superficial parotidectomy. The local recurrence was found 6 years after the initial surgery. The recurrent tumor was removed, and radiotherapy was administered thereafter. The patient has been free from the disease for 33 months since the last treatment. The treatment for the primary lesion is crucial for the prognosis since metastasis to the regional lymph node or to distant region is unusual in PLGA. Although surgical extirpation is the recommended modality for treatment of PLGA, wide resection with a safety margin is often difficult in the parotid gland because of the presence of the facial nerve. Our two cases were successfully treated with surgery and postoperative radiotherapy. Although our literature search revealed 32 previously reported cases of PLGA of the parotid gland, only five of the 32 cases were treated postoperative radiotherapy. We highlight the importance of postoperative radiotherapy for PLGA of the parotid gland.