High Grade Transformation in Mucoepidermoid Carcinoma of the Minor Salivary Gland with Polyploidy of the Rearranged MAML2 Gene

Mucoepidermoid carcinoma (MEC) is the most common malignant tumor of the salivary gland. However, reports of high grade transformation in MEC are extremely rare, and only two cases have so far been described. Recent development of salivary gland pathology revealed recurrent gene rearrangements in many kinds of tumors, including MAML2 fusion of MEC. To date, the MAML2 status of high grade transformed MEC has not been studied. Here we report the first case of minor salivary gland origin high grade transformation in MEC with a MAML2 break apart FISH study. A 73-year-old woman presented with a 1-month history of left mandibular area swelling, and computed tomography and magnetic resonance imaging revealed a mass in the hard palate with various-sized lymphadenopathy of the neck. The resected tumor histologically consisted of two carcinomatous components. Approximately 30% of the tumor showed a conventional MEC feature, while 70% was comprised of a high grade transformed component. In the conventional MEC component, FISH revealed MAML2 rearrangement. High grade transformed cells showed multiple split signals, and the results were interpreted as rearrangement and polyploidy after comparison with 1p/19q FISH as validation. The patient received adjuvant radiation therapy after wide resection with neck dissection and retropharyngeal dissection. Nevertheless, as the remaining tumor grew up rapidly and metastatic lymph nodes were newly revealed, the patient expired 7 months after the diagnosis. We first report regarding a high grade transformation in MEC with polyploidy of the rearranged MAML2 gene and aggressive biological behavior.