Epithelial-myoepithelial carcinoma.

In 2002, a 61-year-old woman was diagnosed in Mexico with a right parotid neoplasm. She underwent a superficial parotidectomy with preservation of the facial nerve. The pathology was reported as an adenocarcinoma. She subsequently underwent 2 weeks of postoperative radiotherapy.

The woman did well until late 2004, when she noticed a rapidly enlarging right facial mass. Examination identified a 4 x 5-cm right facial tumor that involved the preauricular skin, extended to the inferior auricle, and erupted through the skin in the postauricular area (figure 1). The facial nerve was intact bilaterally. Findings on fine-needle aspiration biopsy of the mass and incisional biopsy of the postauricular extension were consistent with apleomorphic adenoma. The benign pathologic diagnosis notwithstanding, the tumor's growth patterns exhibited malignant characteristics.

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The patient underwent a total parotidectomy, partial auriculectomy, and wide excision of the involved preauricular facial skin with preservation of the facial nerve. Intraoperative frozen-section biopsies confirmed the pleomorphic adenoma. The final pathology was reported as an epithelial-myoepithelial carcinoma (EMC). No metastatic carcinoma was seen in six intraparotid lymph nodes, and no perineural or intravascular tumor invasion was identified. In light of the diagnosis, the patient was referred for postoperative radiotherapy.

EMCs account for less than 1% of all salivary gland tumors; when they do occur, most are found in the parotid gland. (1) Other reported sites of EMCs are the palate, base of the tongue, submandibular gland, and lung. EMCs have been associated with hybrid carcinomas. Nagao et al reported 9 cases of hybrid carcinomas of the salivary gland; 3 of these cases occurred in conjunction with an EMC--a basal cell adenocarcinoma in 2 cases and a squamous cell carcinoma in the other. (2)

The differential diagnosis is centered on tumors whose histologic characteristics are similar, such as mucoepidermoid carcinoma, sebaceous cell carcinoma, acinic cell carcinoma, mixed tumor, and metastatic renal cell carcinoma. Histologically, EMCs have a biphasic cell pattern that is characterized by small epithelial cells and large, clear myoepithelial cells. Clear cells contain glycogen, unlike the cells in mucoepidermoid carcinoma, which contain mucin. Low-power magnification of an EMC reveals lobular, pushing borders and coagulative necrosis in the center of the lobules. On immunohistochemistry, the myoepithelial cells stain for S-100 protein and smooth-muscle actin (figure 2).

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EMC is considered a low-grade malignancy. Superficial parotidectomy is the treatment for EMCs of the parotid gland. Tas et al (1) and Kumagai et al (3) each reported a case of EMC of the parotid gland that was treated with superficial parotidectomy; no evidence of recurrence was seen at 21 and 6 months, respectively. In cases of EMC associated with a hybrid tumor, treatment should be geared toward the histologic component that has the higher grade of malignancy.

References

(1.)Tas A, Yagiz R, Altaner S, et al. A case of epithelial-myoepithelial carcinoma of the parotid gland. Kulak Burun Bogaz Ihtis Derg 2003;10:171-4.

(2.) Nagao T, Sugano I, Ishida Y, et al. Hybrid carcinomas of the salivary glands: Report of nine cases with a clinicopathologic, immunohistochemical, and p53 gene alteration analysis. Mod Pathol 2002;15:724-33.

(3.) Kumagai M, Suzuki H, Matsuura K, el al. Epithelial-myoepithelial carcinoma of the parotid gland. Auris Nasus Larynx 2003;30:201-3.

Sofia Avitia, MD; Jason S. Hamilton, MD; Ryan F. Osborne, MD

From the Department of Otolaryngology, Charles R. Drew University of Medicine and Science (Dr. Avitia, Dr. Hamilton, and Dr. Osborne), and the Head and Neck Cancer Center, Cedars-Sinai Medical Center (Dr. Osborne), Los Angeles.