Mimickers of neuroendocrine neoplasms (NEN) include a number of important pitfall tumors. Here, we describe our experience with mesenchymal mimics of NENs to illustrate their spectrum and draw the attention particularly to a group of mesenchymal/non-epithelial neoplasms (MN) that combine epithelioid histology with neuroendocrine (NE-) features and peculiar genetic abnormalities. In a consultation series of 4498 cases collected between 2009 and 2021, 2099 neoplasms expressing synaptophysin and/or chromograninA were reviewed and analyzed. A total of 364 (18%) were diagnosed as non-NENs, while the remaining tumors were NEN. The group of mesenchymal/non-epithelial neoplasms with NE-features (MN-NE) included 31/364 (8%) cases. These mostly malignant neoplasms showed an epithelioid morphology. While all but one tumor expressed synaptophysin, mostly patchy, only 10/29 (34%) co-expressed chromograninA. A total of 13/31 (42%) of the MN-NE showed EWSR1-related gene fusions (6 Ewing sarcomas, 5 clear cell sarcomas, and 1 desmoplastic small round cell tumor, 1 neoplasm with FUS-CREM gene fusion) and 7 (23%) were SWI/SNF (SMARCB1 or SMARCA4)-deficient neoplasms. The remaining MN-NE included synovial sarcoma, sclerosing epithelioid mesenchymal neoplasm, melanoma, alveolar soft part sarcoma, solitary fibrous tumor, and chordoma. A total of 27/31 MN-NE were from the last 8 years, and 6 of them were located in the pancreas. Eleven MN-NE were initially diagnosed as neuroendocrine carcinomas (NECs). MN-NE with epithelioid features play an increasing role as mimickers of NECs. They mostly belong to tumors with gene fusions involving the EWSR1 gene, or with SWI/SNF complex deficiency. Synaptophysin expression is mostly patchy and chromograninA expression is infrequent in MN-NE of this series and data extracted from literature.

神经内分泌肿瘤 (NEN) 的模拟物包括许多重要的陷阱肿瘤。在这里，我们描述了我们对 NEN 间充质模拟物的经验，以说明它们的范围，并特别引起对一组间充质/非上皮肿瘤 (MN) 的关注，这些肿瘤将上皮样组织学与神经内分泌 (NE-) 特征和特殊的遗传异常相结合。在 2009 年至 2021 年间收集的 4498 个病例的咨询系列中，对 2099 种表达突触素和/或嗜铬粒蛋白 A 的肿瘤进行了审查和分析。共有 364 例（18%）被诊断为非 NEN，其余肿瘤为 NEN。具有 NE 特征 (MN-NE) 的间充质/非上皮肿瘤组包括 31/364 (8%) 例。这些主要是恶性肿瘤显示上皮样形态。虽然除了一种肿瘤外，所有肿瘤都表达了突触素 大部分呈片状，只有 10/29 (34%) 共表达 chromograninA。总共 13/31 (42%) 的 MN-NE 显示EWSR1相关基因融合（6 例尤文肉瘤、5 例透明细胞肉瘤和 1 例结缔组织增生性小圆细胞瘤、1 例具有FUS-CREM基因融合的肿瘤）和 7 例（23%）是 SWI/SNF（SMARCB1 或 SMARCA4）缺陷型肿瘤. 其余的 MN-NE 包括滑膜肉瘤、硬化性上皮样间充质肿瘤、黑色素瘤、肺泡软部肉瘤、孤立性纤维瘤和脊索瘤。总共 27/31 MN-NE 来自过去 8 年，其中 6 个位于胰腺中。11 名 MN-NE 最初被诊断为神经内分泌癌 (NEC)。具有上皮样特征的 MN-NE 作为 NEC 的模仿者发挥着越来越大的作用。它们大多属于基因融合涉及EWSR1 的肿瘤基因，或 SWI/SNF 复合体缺陷。突触素表达多呈片状，嗜铬粒蛋白A表达在本系列的MN-NE和文献中提取的数据中很少见。