Myoepithelial Tumor of Soft Tissue

Abstract

Myoepithelial neoplasms represent a heterogeneous group of tumors of which classification is incomplete and evolving. Those of the soft tissues often form genetically distinct subgroups that differ from those arising within salivary glands. Soft-tissue myoepithelial tumors (including mixed tumors that show true glandular or ductal differentiation) exhibit a spectrum of different morphologic patterns, making them difficult to distinguish from a variety of other neoplasms. They have been increasingly shown to harbor genetic fusions involving EWSR1 and partner genes that are not seen in the well-characterized tumor classes involving EWSR1 translocations. We review the spectrum of soft-tissue myoepithelial tumors, discussing recent immunohistochemical and genetic findings and the differential diagnosis.

The spectrum of EWSR1-rearranged neoplasms at a tertiary sarcoma centre; assessing 772 tumour specimens and the value of current ancillary molecular diagnostic modalities

“…Its role in cancer cell progression is still unclear, although it may play a critical role in DNA damage response and cell division (Li et al , 2007; Paronetto, 2013). While initially thought specific for Ewing sarcoma (formerly the Ewing sarcoma/primitive peripheral neuroectodermal tumour (PNET) family of tumours) (Dockhorn Dworniczak et al , 1994), characteristic rearrangements between EWSR1 and partner genes have been documented in both tumours of mesenchymal and non-mesenchymal lineage, including desmoplastic small round cell tumour (DSRCT; Ladanyi and Gerald, 1994; Antonescu et al , 1998), myxoid liposarcoma (MLPS; Panagopoulos et al , 1996; Dal Cin et al , 1997; Hosaka et al , 2002), extraskeletal myxoid chondrosarcoma (EMC; Sciot et al , 1995; Clark et al , 1996), angiomatoid fibrous histiocytoma (AFH; Hallor et al , 2005; Rossi et al , 2007; Thway and Fisher, 2015; Thway et al , 2015b), clear cell sarcoma of soft tissue (CCS; Hisaoka et al , 2008; Wang et al , 2009) and clear cell sarcoma-like tumours of the gastrointestinal tract (CCSLGT; Thway and Fisher, 2012; Wang and Thway, 2015), primary pulmonary myxoid sarcoma (PPMS; Thway et al , 2011), myoepithelial tumours of skin, soft tissue and bone (Antonescu et al , 2010a; Antonescu et al , 2010b; Thway and Fisher, 2014; Thway et al , 2015a), and more rarely in low-grade fibromyxoid sarcoma (LGFMS; Lau et al , 2013) and sclerosing epithelioid fibrosarcoma (SEF; Doyle et al , 2012; Arbajian et al , 2014). EWSR1 rearrangements can be easily detected in the routine setting by fluorescence in situ hybridisation (FISH) with break-apart probes, and corresponding fusion transcripts by reverse transcription–PCR (RT–PCR) studies, usually using commercial probes and primers respectively.…”

Epithelioid malignant peripheral nerve sheath tumor arising in schwannoma

“…However, myoepithelial carcinoma should also display some cytokeratin and EMA positivity, in addition to expression of smooth muscle markers. 14 , 15 Epithelioid sarcoma typically shows strong cytokeratin expression with about 50% also showing strong CD34 positivity. 16 …”

Thoracic Myoepithelial Tumors

“…Other primary thoracic tumors to consider are schwannomas, which can occasionally have myxoid stroma, and primary pulmonary myxoid sarcoma (PPMS), which can have striking morphologic similarity to MTs. Immunohistochemistry can generally resolve this differential, and in difficult cases FISH can also be used to exclude a PPMS, which harbors a characteristic EWSR1-CREB1 fusion 40 . Finally, there are a number of metastatic tumors that can have overlapping morphologic and immunohistochemical features with MTs including metastatic melanoma, matrix producing carcinoma of the breast, ossifying fibromyxoid tumor (OFT), extraskeletal myxoid chondrosarcoma (EMC), clear cell sarcoma (CCS), and Ewing sarcoma.…”