New variants of epithelial-myoepithelial carcinoma: oncocytic-sebaceous and apocrine.
BACKGROUND
Recently described variants of epithelial-myoepithelial carcinoma have not been well characterized but raise a distinct set of differential diagnostic considerations than the classic type.


OBJECTIVE
To report a detailed analysis of oncocytic-sebaceous epithelial-myoepithelial carcinoma (OEMCa) and a similar, but novel, variant, apocrine epithelial-myoepithelial carcinoma (ApEMCa).


METHODS
Clinical, histologic, and immunophenotypic features of 5 OEMCas and 5 ApEMCas were analyzed. Ultrastructural examination was also performed on 3 OEMCa and 1 ApEMCa tumors.


RESULTS
The mean age for OEMCa (74.4 years; range, 58-82 years) was slightly higher than for ApEMCa (61.6; range, 46-79 years). All tumors arose in the parotid glands and demonstrated a multinodular pattern of growth with an average size of 3.3 cm (range, 2.3-6.5 cm). Available follow-up (n = 6; 3 OEMCas, 3 ApEMCas) shows a favorable course (no evidence of disease; mean, 17.4 months). Both were morphologically similar, but only OEMCa had sebaceous elements. Phosphotungstic acid hematoxylin staining, antimitochondrial antibody immunohistochemistry, and ultrastructural examination confirm the abundance of mitochondria in OEMCa but not in ApEMCa. The ductal component in ApEMCa was distinguished from that of OEMCa by apical snouts, intracytoplasmic vacuoles, nuclear pleomorphism, prominent nucleoli, and androgen receptor immunoreactivity.


CONCLUSIONS
Oncocytic-sebaceous epithelial-myoepithelial carcinoma and ApEMCa should be considered in the differential diagnosis of oncocytic/oncocytoid salivary gland tumors. Oncocytic-sebaceous epithelial-myoepithelial carcinoma morphology may reflect a senescent phenotype, similar to other oncocytic lesions. The ductal component of ApEMCa shares some similarities with salivary duct carcinoma and supports the notion that epithelial-myoepithelial carcinoma can serve as the progenitor tumor for hybrid tumors.
Seethala
Raja R
RR
Department of Pathology and Laboratory Medicine, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania 15213, USA. seethalarr@upmc.edu
Richmond
Jeffrey A
JA
Hoschar
Aaron P
AP
Barnes
E Leon
EL
D018266:Adenocarcinoma, Sebaceous / Q000473:pathology*; D000368:Aged; D000369:Aged, 80 and over; D001050:Apocrine Glands / Q000473:pathology*; D002277:Carcinoma / Q000473:pathology*; D003937:Diagnosis, Differential; D006801:Humans; D007150:Immunohistochemistry; D046529:Microscopy, Electron, Transmission; D008875:Middle Aged; D009208:Myoepithelioma / Q000473:pathology*; D010307:Parotid Neoplasms / Q000473:pathology*