Department of Pathology, Faculty of Medicine in Pilsen, Charles University.
Bioptic Laboratory Ltd.
Am J Surg Pathol. 2021 Jan;45(1):1-13. doi: 10.1097/PAS.0000000000001591.
Myoepithelial carcinoma of salivary glands is an underrecognized and challenging entity with a broad morphologic spectrum, including an EWSR1-rearranged clear cell variant. Myoepithelial carcinoma is generally aggressive with largely unknown genetic features. A retrospective review of Salivary Gland Tumor Registry in Pilsen searching for the key words "clear cell myoepithelial carcinoma," "hyalinizing clear cell," and "clear cell malignant myoepithelioma" yielded 94 clear cell myoepithelial carcinomas (CCMCs) for molecular analysis of EWSR1 rearrangement using fluorescence in situ hybridization (FISH). Tumors positive for EWSR1 gene rearrangement were tested by next-generation sequencing (NGS) using fusion-detecting panels. NGS results were confirmed by reverse-transcription polymerase chain reaction or by FISH. Twenty-six tumors originally diagnosed as CCMC (26/94, 27.6%) revealed split signals for EWSR1 by FISH. Six of these tumors (6/26, 23%) displayed amplification of the EWSR1 locus. Fifteen cases were analyzable by NGS, whereas 9 were not, and tissue was not available in 2 cases. None of the CCMCs with EWSR1 rearrangements detected by FISH had an EWSR1 fusion transcript. Fusion transcripts were detected in 6 cases (6/15, 40%), including LIFR-PLAG1 and CTNNB1-PLAG1, in 2 cases each, and CHCHD7-PLAG1 and EWSR1-ATF1 fusions were identified in 1 case each. Seven cases, including those with PLAG1 fusion, were positive for PLAG1 rearrangement by FISH, with notable exception of CHCHD7-PLAG1, which is an inversion not detectable by FISH. One single case with EWSR1-ATF1 fusion in NGS showed ATF1 gene rearrangement by FISH and was reclassified as clear cell carcinoma (CCC). In addition, another 4 cases revealed ATF1 rearrangement by FISH and were reclassified as CCC as well. Moreover, 12/68 (17%) CCMCs with intact EWSR1 gene were selected randomly and analyzed by NGS. PLAG1 fusions were found in 5 cases (5/12, 41.6%) with LIFR (2 cases), FGFR1 (2 cases), and CTNNB1 (1 case) as partner genes. Overall, PLAG1 gene rearrangements were detected in 10/38 (26%) tested cases. None of the tumors had SMARCB1 loss by immunohistochemistry as a possible explanation for the EWSR1 abnormalities in FISH. Novel findings in our NGS study suggest that EWSR1-FISH positive CCMC is a gene fusion-driven disease with frequent oncogenic PLAG1 fusions, including LIFR-PLAG1 and CTNNB1-PLAG1 in most cases. Productive EWSR1 fusions are found only in a minority of EWSR1-ATF1-rearranged cases, which were in part reclassifiable as CCCs. Detectable EWSR1-FISH abnormality in CCMCs without gene fusion perhaps represents a passenger mutation with minor or no oncologic effect.
涎腺肌上皮癌是一种认识不足且具有挑战性的实体瘤，其形态学表现广泛，包括 EWSR1 重排的透明细胞变异型。肌上皮癌通常具有侵袭性，其遗传特征大多未知。对普日布拉姆唾液腺肿瘤登记处进行了回顾性研究，检索关键词为“透明细胞肌上皮癌”、“透明细胞性玻璃样变”和“透明细胞恶性肌上皮瘤”，共发现 94 例透明细胞肌上皮癌（CCMC），采用荧光原位杂交（FISH）对 EWSR1 重排进行分子分析。对 EWSR1 基因重排阳性的肿瘤进行下一代测序（NGS），使用融合检测面板。NGS 结果通过逆转录聚合酶链反应或 FISH 进行确认。最初诊断为 CCMC 的 26 例肿瘤（26/94，27.6%）经 FISH 检测显示 EWSR1 信号分离。其中 6 例（6/26，23%）显示 EWSR1 基因座扩增。15 例可进行 NGS 分析，9 例不可分析，2 例无组织。经 FISH 检测发现 EWSR1 重排的 CCMCs 均未检出 EWSR1 融合转录本。在 6 例（6/15，40%）中检测到融合转录本，包括 LIFR-PLAG1 和 CTNNB1-PLAG1 各 2 例，CHCHD7-PLAG1 和 EWSR1-ATF1 融合各 1 例。包括 PLAG1 融合在内的 7 例 FISH 检测阳性的病例，PLAG1 重排阳性，除了 CHCHD7-PLAG1 外，这是一种不可检测的倒置，FISH 检测结果为阴性。在 NGS 中发现的 EWSR1-ATF1 融合的单个病例，通过 FISH 显示 ATF1 基因重排，被重新分类为透明细胞癌（CCC）。此外，另外 4 例 FISH 检测到 ATF1 重排，也被重新分类为 CCC。此外，随机选择了 68 例 EWSR1 基因完整的 CCMC 中的 12 例进行 NGS 分析。在 5 例（5/12，41.6%）中发现了 PLAG1 融合，其伙伴基因为 LIFR（2 例）、FGFR1（2 例）和 CTNNB1（1 例）。总体而言，在 38 例接受检测的病例中（26%）发现了 PLAG1 基因重排。免疫组织化学检测未发现任何肿瘤存在 SMARCB1 缺失，这可能是 FISH 中 EWSR1 异常的可能解释。我们的 NGS 研究中的新发现表明，EWSR1-FISH 阳性的 CCMC 是一种基因融合驱动的疾病，常伴有致癌性 PLAG1 融合，大多数病例为 LIFR-PLAG1 和 CTNNB1-PLAG1。在部分 EWSR1-ATF1 重排病例中发现有功能的 EWSR1 融合，这些病例部分可重新分类为 CCC。在没有基因融合的 CCMC 中，可检测到 EWSR1-FISH 异常，可能代表一种乘客突变，其具有较小或无致癌作用。
