Epithelial-myoepithelial carcinoma (EMC) is a very rare, low grade neoplasm, that represents less than 1% of all salivary gland tumors [1,2,4] and can occur in any site with salivary or mucoserous glands, including in the respiratory tract [2,7]. EMC has a predilection for the major salivary glands, in which 60-75% are in the parotid gland . This neoplasm has a slight elderly female predominance with range of age between 6th and 7th decades [4,7]. The usual clinical presentation consists of a painless, slow growing mass that can have ill-defined margins.
On imaging, these lesions may demonstrate well defined smooth margins with mild enhancement on CT and low to intermediate T1 signal with moderately increased T2 signal on MRI .
Grossly, the lesion is usually well circumscribed but unencapsulated, solid, firm, tan white to yellow mass ranging in size from 1-12 cm in greatest dimension. Minor salivary gland involvement may be associated with ulceration .
The aspirate smears are generally cellular with no specific pattern and depicts a biphasic epithelial (small cells) and myoepithelial (large/clear cells) populations. However, this biphasic arrangement may be subtle or absent, as the clear cells have fragile cytoplasm and often appear as naked nuclei [4,8].
Histologically, EMC is a low-grade biphasic tumor composed of ductal epithelial cells and myoepithelial cells. The tumor nests frequently have an organoid arrangement but may also have a cystic, papillary or solid pattern. The tumor nests are variably separated by a thin fibrovascular to loose myxoid stroma with base-membrane like material that maybe thickened, appearing as eosinophilic, hyalinized membrane . The histologic variants are oncocytic (needs at least 50% of oncocytic component ), dedifferentiated, EMC with myoepithelial neoplasia, EMC carcinoma ex- pleomorphic carcinoma, papillary and sebaceous differentiation .
Treatment and prognosis
Complete surgical excision is the treatment of choice and is often curative [2,8]. Adjuvant therapy is utilized in patients whose tumors cannot be completely excised. Local recurrence is frequent, seen in 30-50% of cases [4,8]. Metastatic tumor may occur in up to 20% of cases and often occurs in regional (cervical or periparotid lymph nodes). Less commonly, metastases have been reported in lungs, kidney and brain .
In general, prognosis is very good with a 5 years survival rate reported to be 80-94% [2,8]. Factors associated with adverse prognosis include large tumor size, rapid growth, occurrence in a minor salivary gland, solid growth pattern, nuclear atypia in more than 20% of tumor, DNA aneuploidy and high proliferative activity . Factors that impact on disease free survival are positive margin status, presence of angiolymphatic invasion, necrosis and myoepithelial anaplasia [2,8].
Epithelial myoepithelial carcinoma may arise from a preexisting pleomorphic adenoma (PA). This can be ascertain either through morphologic evidence or presence of PLAG1 (8q12) or HMGA2(12q13) rearrangements. A small subset demonstrate HRAS mutations [1,3].