Myoepithelial Carcinoma.

Area of Science:

• Oncology
• Pathology
• Genetics

Background:

• Myoepithelial carcinoma (MECA) presents diagnostic challenges due to histological overlap with other salivary gland tumors, notably pleomorphic adenoma.
• MECA exhibits characteristic cellular, uniform growth of myoepithelial cells with a multinodular, expansile, invasive pattern and zonal cellular distribution.
• This malignancy can arise independently (de novo) or as a transformation from a pre-existing pleomorphic adenoma (carcinoma ex pleomorphic adenoma).

Purpose of the Study:

• To delineate the key histological, immunohistochemical, and genetic features of myoepithelial carcinoma.
• To identify prognostic factors associated with clinical outcomes in MECA.
• To establish criteria for high-grade classification of MECA.

Main Methods:

• Histopathological examination of MECA cases.
• Immunohistochemical analysis for cytokeratins and myoepithelial markers (e.g., S100).
• Genetic analysis to identify common alterations like PLAG1 fusion.

Main Results:

• MECA shows positive staining for cytokeratins and at least one myoepithelial marker.
• PLAG1 fusion represents the most frequent genetic alteration found in MECA.
• The presence of carcinoma ex pleomorphic adenoma and necrosis correlates with adverse clinical outcomes and indicates high-grade disease.

Conclusions:

• Myoepithelial carcinoma requires careful histological and immunohistochemical evaluation to distinguish it from benign mimics.
• Genetic alterations, particularly PLAG1 fusion, are important in the characterization of MECA.
• Necrosis and transformation from pleomorphic adenoma are critical indicators for grading and predicting prognosis in myoepithelial carcinoma.