Myoepithelial tumor of soft tissue and bone: A current perspective

Abstract

Myoepithelial tumor (MET) of soft tissue and bone is an unusual tumor of uncertain differentiation and histogenesis, but lately has been recognized as a distinct tumor entity. This tumor forms a morphologic continuum with a mixed tumor and a parachordoma, but is different from an extra-axial chordoma or chordoma periphericium. METs display a range of histopathologic features, including architectural arrangements/growth patterns, cell types and intervening stroma, leading to their several differential diagnoses. Presently, moderate nuclear atypia is the acceptable criterion to differentiate a myoepithelial carcinoma from a myoepithelioma. Immunohistochemical (IHC) stains, including epithelial antibody markers, along with S100 protein and GFAP are necessary in confirming a diagnosis of a MET. Certain METs are associated with loss of INI1/SMARCB1. Lately, certain specific “molecular signatures” been described underlying METs, identification of which that can further aid in their accurate diagnosis and in differentiating these tumors from their diagnostic mimics. Complete surgical resection forms the treatment mainstay, irrespective of a myoepithelioma or a myoepithelial carcinoma. This review will focus upon clinicopathologic, immunohistochemical and molecular features of METs of soft tissue and bone, along with their differential diagnoses and diagnostic implications.