EWSR1‐ATF1 fusion is a novel and consistent finding in hyalinizing clear‐cell carcinoma of salivary gland

Abstract

Hyalinizing clear-cell carcinoma (HCCC) is a rare, low-grade salivary gland tumor with distinctive clear-cell morphology and pattern of hyalinization as well as focal mucinous differentiation. However, histological overlap exists with other salivary gland tumors, such as epithelial-myoepithelial carcinoma (EMCa), salivary myoepithelial carcinoma, and mucoepidermoid carcinoma (MEC). The potential relationship between HCCC and its morphological mimics has not been yet investigated at the genetic level. In this study, we conducted a molecular analysis for the presence of rearrangements in MAML2, commonly seen in MECs, and EWSR1, involved in "soft tissue myoepithelial tumors" (SMET) by fusion with POU5F1, PBX1, or ZNF444. Fluorescence in situ hybridization (FISH) was performed on 23 HCCC cases for abnormalities in MAML2, EWSR1, FUS, POU5F1, PBX1, and ZNF444. FISH for MAML2 was negative in all cases (0 of 14), including those with mucinous differentiation (0 of 7). An EWSR1 rearrangement was identified in 18 of 22 HCCCs (82%), while no break-apart signals were seen in FUS, POU5F1, PBX1, or ZNF444. 3'RACE on an EWSR1 rearranged HCCC identified an EWSR1-ATF1 fusion, which was confirmed by RT-PCR. ATF1 involvement was further confirmed by FISH analysis in 13 of 14 EWSR1-rearranged HCCC cases (93%). In contrast, all control cases tested, including among others 5 EMCa and 3 MEC with clear cells, were negative for EWSR1 and ATF1 rearrangements. The presence of EWSR1-ATF1 fusion in most HCCCs reliably separates these tumors from its histological mimics. The distinction from MEC is particularly important, as conventional MEC grading schemes overgrade these indolent HCCCs, potentially impacting on treatment.

FUS rearrangements are rare in ‘pure' sclerosing epithelioid fibrosarcoma

“…Other rearrangements involving identical loci and the same recurrent translocations can be shared by different sarcomas, lymphomas, and carcinomas. [24][25][26] Similar to EWSR1, rearrangements in FUS have been reported in multiple sarcomas, including low-grade fibromyxoid sarcoma, myxoid liposarcoma, angiomatoid fibrous histiocytomas, and Ewing sarcoma. 25 Both angiomatoid fibrous histiocytoma and clear cell sarcoma harbor the same two translocation variants, EWSR1-ATF1 t(12;22)(q13;q12) and EWSR1-CREB1 t(2;22)(q34;q12), yet both are phenotypically distinct from each other with distinctly different clinical courses.…”

“…[27][28][29][30] More recently, recurrent EWSR1-CREB1 translocations have also been identified in hyalinizing clear cell carcinoma of the salivary gland. 26 Other examples include involvement of ALK-TPM3 in inflammatory myofibroblastic tumor and anaplastic large cell lymphomas, and ETV6-NTRK in infantile fibrosarcoma, secretory breast carcinomas, and acute myeloid leukemia. 24,31 These findings challenge the previously held notion that recurrent translocations are unique to a particular sarcoma or tumor class.…”

Myoepithelial Neoplasms of Soft Tissue: An Updated Review of the Clinicopathologic, Immunophenotypic, and Genetic Features

“…Documented fusion partners thus far include POU5F1 (6p21), PBX1 (1q23), ZNF444 (19q23), ATF1 (12q13) and PBX3 (9q33) [22,24,25]. Homozygous deletion of the SMARCB1 gene has recently been reported in 3/5 cases of myoepithelial carcinoma lacking EWSR1 gene rearrangement [26].…”

“…EWSR1-rearrangement occurs in up to 44 % of cutaneous myoepithelial tumors [25] (including cutaneous syncytial myoepithelioma [7]). While EWSR1 rearrangement is present in hyalinizing clear cell carcinoma [24], EWSR1 rearrangement has not been identified to date in other salivary neoplasms, including myoepithelial tumors [27,28] (see Addendum).…”

Morphology in Conjunction with Immunohistochemistry is Sufficient for the Diagnosis of Mammary Analogue Secretory Carcinoma

“…There are a handful of salivary gland tumors that have been demonstrated to have recurring cytogenetic abnormalities including adenoid cystic carcinomas [t(6;9) (MYB-NFIB)] [8][9][10], mucoepidermoid carcinomas [t(11:19) (MECT1-MAML2)] [11,12], pleomorphic adenomas (PLAG1 and HMGA2 rearrangements) [13][14][15][16][17], and hyalinizing clear cell carcinoma [t(12;22) (EWSR1-ATF)] [18,19]. In the majority of these tumors, the morphology is distinctive enough to allow for a diagnosis and molecular confirmation is typically not necessary.…”