A Case of Dedifferentiated Epithelial Myoepithelial Carcinoma Presenting as a High-grade Parotid Carcinoma

<p>In the treatment of salivary gland cancer, radical resection with negative surgical margins is paramount in determining the patient’s prognosis, and therefore, the indication for concomitant resection of the facial nerve should be carefully considered, based on not only the findings on preoperative examination, but also on the intraoperative findings. We report a case of high-grade parotid carcinoma with positive surgical margins that resulted from discrepancies between the findings during preoperative treatment planning and the intraoperative findings, which led to a poor prognosis. In addition, histopathology revealed a rare tumor, namely, dedifferentiated epithelial myoepithelial carcinoma (EMC). Therefore, in this case report, we also review this rare disease entity. The patient was a 58-year-old man who presented with a swelling below the left ear that he had first noticed about 5 months prior to his first visit to our department, and he was referred to us with a suspected left parotid tumor. Physical examination revealed a hard mass with poor mobility below the left ear and multiple enlarged lymph nodes at levels II and III in the left cervical region. CT and MRI showed two irregular masses with poor enhancement within the left parotid gland, one 3.4 cm in diameter and the other 3.2 cm in diameter, and enlarged lymph nodes at levels I-III of the left neck. FDG-PET/CT showed accumulation in the same masses and in the left cervical enlarged lymph nodes. Core needle biopsy of the left parotid tumor revealed poorly differentiated carcinoma, and a total left parotidectomy was performed with left cervical dissection. Histopathology showed a bilayer of cuboidal cells with eosinophilic spherocytes inside and bright cells outside, and a focal and dense infiltrative growth of atypical cells containing enlarged nuclei with prominent nucleoli; based on the findings, we made the diagnosis of dedifferentiated EMC. Since the tumor resection margins were partially positive, and multiple metastases to the dissected lymph nodes and some extranodal invasion were also observed, radiation therapy (60 Gy) was added as adjuvant therapy. One year after the completion of radiotherapy, there was no apparent disease recurrence. Herein, we described a case of dedifferentiated EMC presenting as a high-grade parotid carcinoma. In the treatment of salivary gland carcinoma, radical resection with negative surgical margins is crucial in determining the patient’s prognosis. Therefore, the indication for resection of the facial nerve should be considered based on the distance between the facial nerve and the tumor, the tumor histology, and the malignancy grade of the salivary gland cancer, and sometimes it is considered necessary not to hesitate to perform resection of the facial nerve in order to achieve a complete resection. While some reports of cases of dedifferentiated EMC, which are considered to be very rare, have been published previously, a larger number of cases should be accumulated to further elucidate the characteristics of dedifferentiated EMC.</p>