Myoepithelioma of the parotid gland with extensive adipocytic metaplasia: Report of a case with intriguing aspects on fine needle aspiration and p63 immunohistochemical expression.
CSM has unique morphologic and immunohistochemical features, characterized by intradermal syncytial growth of spindled, ovoid, and histiocytoid cells and consistent staining for S-100 protein and EMA, and differs from other myoepithelial tumors by showing only infrequent keratin staining.
Rearrangement of the EWSR1 gene is now known to occur in up to half of all skin and soft tissue myoepithelial tumors, with a wide family of documented fusion partners.
EWSR1 rearrangement is present in a subset of myoepithelial tumors of salivary glands with variable morphology and does not correlate with clinical behavior.
Herein we describe a soft tissue myoepithelioma arising in the pelvis with an EWSR1-ATF1 fusion, therefore extending the spectrum of partner genes of EWSR1.
The SEER database was queried to find cases of mesenchymal tumors associated with EWSR1 translocations: Ewing sarcoma; clear cell sarcoma; extraskeletal myxoid chondrosarcoma; myxoid liposarcoma; desmoplastic small round cell tumor; and myoepithelial tumor.
EWSR1-POU5F1 fusion in soft tissue myoepithelial tumors. A molecular analysis of sixty-six cases, including soft tissue, bone, and visceral lesions, showing common involvement of the EWSR1 gene.
Recently, EWSR1 rearrangement has been described in a subset of soft tissue myoepithelial tumors, whereas the cutaneous counterparts showed this aberration in a minority of cases.
EWS RNA-binding protein 1 gene (EWSR1) rearrangement is found in 45% of cutaneous, soft tissue and bone myoepithelial neoplasms, and pleomorphic adenoma gene 1 (PLAG1) aberrations are found in 37% of EWSR1-negative soft tissue myoepitheliomas.
The molecular confirmation of diagnosis using RT-PCR is necessary to do the differential diagnosis with other entities, in particular with myoepithelioma that shows similar morphological features and EWSR1 and FUS genes rearrangement.
Considering the unusual location, we additionally performed a cytogenetic analysis to confirm the presence of the EWSR1 gene rearrangement, which is a genetic characteristic of myoepithelioma.
To evaluate if this is a recurrent event, an additional cohort of 22 EWSR1-rearranged ME cases lacking a fusion partner were screened by FISH for abnormalities in PBX3 gene.
Sharing the unusual clinicopathologic features and the novel fusion, these 2 cases probably represent a distinct tumor entity, whose relationship with myoepithelial tumors and tumorigenic mechanisms exerted by the OGT-FOXO3 fusion remain to be studied.