Epithelial myoepithelial carcinoma represents 1% of all
salivary gland tumors. Epithelial myoepithelial carcinoma is a
rare salivary gland neoplasm that chiefly localizes in the
parotid gland. It predominantly involves females. It is
generally seen in the sixth decade
1-6. Our case was a- 67
year old male patient and the lesion was on his right parotid
gland. Radiologic imaging shows an irregular and
heterogeneous mass
4. The radiologic imagings indicated that
there were partially cystic and solid components in the tumor.
The histologic appearance of epithelial myoepithelial
carcinoma varies not only from carcinoma to carcinoma but
also within the same neoplasm. Epithelial myoepithelial
carcinoma is histologically most significant for its biphasic
cellular profile
1,5. In its classic form, this carcinoma
demonsrates a nodular growth pattern composed of well
defined tubules of varying size lined by two layers of cells.
The inner layer is composed of cuboidal to low columnar
ductal cells with an eosinophilic cytoplasm. The outer layer
consists of ovoid cells with pale, abundant, clear cytoplasm
overlying an external well developed basement membrane. The
cuboidal cells have a finely granular dense eosinophilic
cytoplasm and a central or basal round nucleus. The clear cells
are polyhedral with well defined borders and eccentric
vesicular nuclei. There is minimal nuclear pleomorhpism;
necrosis and mitosis can be seen infrequently. The
myoepithelial cells may also be arranged in solid sheets or
nests without ducts. In some carcinomas the biphasic pattern is
less apparent and the appearance is dominated by solid groups of clear cells separated by fibroconnective tissue or trabeculae
of clear cells separated by a thick basal membrane
1.
Myoepithelial carcinoma and myoepithelioma have only
myoepithelial cell proliferation. We observed a dual cell
population in our slides contrary to myoepithelioma or
myoepithelial carcinoma. They consisted of epithelial ductal
cells which were surrounded by clear cells with eccentric
vesicular nuclei. In some sections there were solid sheets of
clear cells with separated fibrous tissue. The differential
diagnosis includes other clear cell tumors, such as acinic cell
carcinoma, mucoepidermoid carcinoma, clear-cell variant of
oncocytoma, as well as metastatic renal cell carcinoma.
Careful sampling of the salivary lesion is generally useful in
demonstrating the biphasic component as in our case. Wang et
al. have shown that in a comparative meta-analytic study of the
clear-cell salivary gland, neoplasms, including EMEC are
present; it had a significantly higher local recurrence rate, but a
lower capablity of distant metastasis than the others after
resection. They also had concluded that there was no specific immunmarker for diagnosis
7. In a case report of epithelial
myoepithelial carcinoma of the base of the tongue, the patient
had been treated with neoadjuvant chemotherapy followed by
radiotherapy
8. At the present time, the common consensus is
that surgery is the treatment of choice. In this case superficial
parotidectomy was performed because histologic examination
of the parotidectomy specimen showed no perineural or
vascular invasion. Surgical margins were also intact. Local
recurrence rates range from 17- 60%
1,6,7,9. We did not
observe recurrence during a sixteen month follow up.
In conclusion, salivary gland neoplasms sometimes can
be difficult to recognize because of their rarity. Not only
should pathologists always be alert in the diagnosis of these
neoplasms, but also clinicians should closely follow up on
those patients diagnosed as EMEC because of the uncertainty
of our knowledge about the behaviour of these unusual
neoplasms.