Bull Tokyo Dent Coll (2014) 55(1): 25–31 Case Report A Case of Mucoepidermoid Carcinoma with Clear Cell Components Occurring in Retromolar Region Nobuharu Yamamoto1), Yukio Watabe1), Masashi Iwamoto1), Kenichi Matsuzaka2) and Takahiko Shibahara1) 1) Department of Oral and Maxillofacial Surgery, Tokyo Dental College, 1-2-2 Masago, Mihama-ku, Chiba 261-8502, Japan 2) Department of Clinical Pathophysiology, Tokyo Dental College, 1-2-2 Masago, Mihama-ku, Chiba 261-8502, Japan Received 12 April, 2013/Accepted for publication 20 September, 2013 Abstract Mucoepidermoid carcinomas in the minor salivary glands usually originate in the palatine gland, and their occurrence in the retromolar region is rare. We report a rare case of mucoepidermoid carcinoma with clear cell components occurring in the retromolar region. The patient was a 63-year-old woman referred to our hospital with the chief complaint of a painless mass in the right retromolar region initially found during treatment at a local dental clinic. The 20210-mm mass was well-defined, elastic, and flexible. The surface of the mucosa was healthy. The mass was clinically diagnosed as a gingival benign tumor in the right retromolar region. There were no significant findings in the patient’s medical history. The tumor was resected under local anesthesia. Histopathology revealed that squamoid cells, undifferentiated intermediate cells, and clear cells were dominant, with mucus-producing cells in some areas. A mucoepidermoid carcinoma with clear cell components was diagnosed. There were no signs of recurrence or metastasis at 15 months postoperatively and the patient’s progress has been satisfactory. Because the tumor was a painless, slow-growing mass, it was clinically diagnosed as a benign tumor of the gingiva, and resection was performed under local anesthesia without performing a biopsy. However, even if a mass in the retromolar region is clinically diagnosed as a benign tumor, the course of treatment should be decided after performing fine-needle aspiration cytology, taking into consideration the possibility of mucoepidermoid carcinoma. Key words: Mucoepidermoid carcinoma — Clear cell — Retromolar region — Salivary gland tumor Introduction ductal epithelium-derived tumor composed of mucus-producing, squamoid, and interme- Named by Stewart et al.22) in 1945, a muco- diate cells. Among the major salivary glands, epidermoid carcinoma is a salivary gland it occurs most frequently in the parotid gland 25 26 Yamamoto N et al. (about 80%), and is rare in the submandibular (approximately 10%) and sublingual glands (approximately 5%). In the minor salivary glands, mucoepidermoid carcinomas mainly derive from the palatine gland, but are also found in the tongue, oral floor, gingiva, and buccal mucosa1). Development in the retro- molar or buccal regions, or inside the jaw bone, however, is rare9,10). Histologically, they are classified as follows: well-differentiated (low- grade malignancy), moderately-differentiated (intermediate-grade malignancy), and poorly 1,8) differentiated (high-grade malignancy) . One Fig. 1 Oral image obtained at second visit report has shown that poorly-differentiated Well-defined, flexible, 20210-mm mass was (high-grade) mucoepidermoid carcinomas are observed in right retromolar region. Surface rare, and that the well-differentiated type (low- mucosa was healthy. grade malignancy) predominates, especially in tumors developing in the minor salivary glands13). Here, we report a case of an mucoepider- 2b). Although it was close to the mandible, moid carcinoma with clear cell components there appeared to be no evidence of bone that showed a comparatively low degree of destruction (Fig. 2a) and a benign tumor was differentiation and originated in the retro- suspected. molar salivary gland. When the patient first visited our hospital, the mass was clinically diagnosed as gingival benign tumor in the right retromolar region. Case At the first medical examination in November 2010, surgical resection was recommended, In November 2010, a 63-year-old woman but due to the patient’s own decision, she visited a nearby dental clinic, where a mass stopped coming to the hospital. In November was detected in the right retromolar region 2011, the patient revisited our hospital, with during treatment. She was subsequently the size of the mass showing no change. In referred to our hospital for a more detailed January 2012, the mass was resected under examination. Her chief complaint was a mass intravenous anesthesia as an outpatient pro- in the right retromolar region. Here medical cedure. An electrotome was used to incise only history showed no remarkable findings. the epithelial layer of the entire periphery Her facial appearance was symmetrical. of the mass and surgical scissors to dissect She reported no pain, and no swelling was the mass cleanly. The lesion was covered with observed in the right submandibular lymph a capsule and showed no adhesion to the nodes. A 20210-mm, well-defined, elastic, lingual nerve or blood vessels (Fig. 3). The mobile, and painless mass was observed in entire tumor was resected and a 3-0 nylon the right retromolar region. No fluctuation thread used to suture the resected area. The was observed on palpation, and the mucosa resected lesion was 20215-mm; it was covered was healthy (Fig. 1). Magnetic resonance imag- with a capsule, had an asymmetrical and ing revealed a well-defined, 1028210-mm uneven surface, and was solid but elastic on mass in the right submandibular retromolar the inside. region with a smooth periphery (Fig. 2). The Histopathological findings (Figs. 4a, 4b) mass was isointense to muscle on T1W1 and predominantly revealed squamoid (arrow A), heterogeneous hyperintense on T2W1 (Fig. undifferentiated intermediate, and clear cells Mucoepidermoid Carcinoma with Clear Cell Components 27 Fig. 2 Preoperative MRI image a, b: 1028210-mm mass in right submandibular retromolar region was well-defined with smooth periphery. a: Mass was close to mandible, but no clear evidence of bone destruction. b: Mass was isointense to muscle on T1W1 and heterogeneous hyperintense T2W1. Fig. 3 Inside oral cavity and resected specimen postoperatively Tumor was easily resected. It comprised 20215-mm mass, covered with capsule; it had asymmetrical and uneven surface, and was elastic. When tumor was cut in center, inside was solid and yellow in color. (arrow B); mucus-producing cells were also ing with PAS revealed positive staining for observed in some areas. Therefore, the tumor glycogen inside the cells. Staining was positive was diagnosed as a clear cell variant of for keratin and negative for S-100 or GFAP. In mucoepidermoid carcinoma. Histochemistry addition, because the labeling index of Ki-67 with mucicarmine revealed positive staining was low, the growth potential was determined for mucus-producing cells (Figs. 5a, 5b); stain- to be low. At 15 months postoperatively, no 28 Yamamoto N et al. Fig. 4 H-E staining a: Tumor was formed of fibro-connective tissue lined with parakeratotic stratified squamous epithelium (arrow A). Tumor cells were lined with incomplete thin capsule. They were lobular, solid, and had fine layer of fibro-connective tissue, forming cobblestone appearance in subepithelial connective tissue layer. Atypical glandular cavities of various sizes had formed in parenchyma of tumor. Tumor cells were small and displayed following wide range of characteristics: circular nucleus, eosinophilic cells in dense cobblestone arrangement, and clear cells (arrow B). b: In addition, there were spindle-shaped cells, larger cells that appeared to have mucus inside, and concentric formed crystalloids. Cell nuclei had deeply-stained nuclear chromatin, hyper- trophied nuclear body, and cellular atypia, with an increased N/C rate. Clear cell variant of mucoepidermoid carcinoma was diagnosed based on the following findings: squamoid, undifferentiated intermediate, and clear cells were dominant, with mucus-producing cells seen in some parts. Fig. 5 Histochemical staining Mucicarmine-positive mucus-producing cells (arrow) were observed sporadically or agglomerated in some areas. sign of recurrence or metastasis has been tasis have been reported8,18), and in the 1991 observed (Fig. 6). WHO Classification18) of Tumors, they were classified as mucoepidermoid carcinoma. In the 2005 WHO Classification1), they were Discussion classified into three different types depend- ing on the correlation between the cell distri- Mucoepidermoid carcinomas, originally bution ratio and degree of malignancy: well- known as mucoepidermoid tumors, are benign. differentiated (low-grade malignancy), in which Nevertheless, cases of recurrence and metas- more than 50% of the tumor is comprised Mucoepidermoid Carcinoma with Clear Cell Components 29 dominating. In addition, there was only very little evidence of cyst formation, so it was diagnosed as the clear cell variant of muco- epidermoid carcinoma according to the WHO Classification18). Nonetheless, the possibility of a transition from clear cell components to clear cell variant was recognized. A post- operative whole body PET-CT scan revealed no sign of new tumor formation, including renal metastases. The disease duration of mucoepidermoid carcinoma is reported to be between 8 days to 34 years, with an average of 22 months2). However, in the present case, disease duration was 1 to 2 years. Such mucoepidermoid carcinomas with clear cell components, a type of mucoepidermoid car- Fig. 6 Inside oral cavity at 15 months postoperatively