皮肤滑融性肌上皮瘤(CSM)是皮肤罕见的滑融性肌上皮瘤变体，其特点为间皮内纤维细胞的细胞团生长，具有EMA和S100阳性以及不经常表达角蛋白的免疫表型。尽管CSM最初被描述为一种皮肤肿瘤，但后来已报道了骨骼方面的非皮肤个案。我们旨在通过一项大型多机构研究，调查该变体在所有解剖部位的临床病理特征。我们从档案中收集了共计24例滑融性生长的肌上皮瘤。肿瘤发生于12名男性和12名女性患者（男：女=1:1），中位年龄为31岁（范围，9-69岁）。尽管大多数肿瘤（75%，n=18）发生在皮肤，但有显著的一部分（25%，n=6）发生在非皮肤部位，包括骨骼（n=3），支气管/气管（n=2）和胫骨/腓骨骨间膜（n=1）。肿瘤大小范围从0.4到5.9厘米不等。临床随访（7例患者；随访期14-202个月，中位56.5个月）显示，一例患者在不完全切除皮肤后8年出现单个局部复发，但没有转移；所有患者在最后的随访中均存活且无疾病证据。组织学上，所有肿瘤在低倍镜下呈粉红色，其特点为细胞团的同步生长，细胞呈卵圆形、纺锤形或组织细胞样，胞质呈玫瑰红色，有明显的周围血管旁淋巴浆细胞性炎症。其中三分之一的病例出现脂肪细胞分化（8/24）。罕见的细胞学异常可见，但与增加的有丝分裂活性无关。所有肿瘤均表达S100、SMA和/或EMA。大多数病例中不表达角蛋白。我们进行了16例病例的分子分析，全部显示出EWSR1重排。其中15/15（100%）携带EWSR1::PBX3融合基因，而只有1例进行了EWSR1 FISH分子研究。滑融性肌上皮瘤是一种罕见但可辨识的肌上皮瘤形态变异，可能对皮肤有偏好，但也可发生在不同的非皮肤部位。我们的系列研究提供了证据，支持对术语“皮肤滑融性肌上皮瘤”的重新评估，因为我们系列研究中有25%的患者出现非皮肤肿瘤；因此，我们提议将术语“滑融性肌上皮瘤”用于帮助病理学家识别和避免在涉及非皮肤例子时可能造成混淆的术语。滑融性肌上皮瘤的行为，无论它发生在皮肤或非皮肤部位，都是温和的，也许是良性的，具有局部复发的小潜力。©2023.本文作者独家许可Springer-Verlag GmbH Germany及Springer Nature。

Cutaneous syncytial myoepithelioma (CSM) is a rare myoepithelioma variant of skin, characterized by intradermal syncytial growth of spindle cells with a distinct immunophenotype of EMA and S100 positivity and infrequent keratin expression. While CSM was first described as a cutaneous tumor, singular non-cutaneous cases have since been reported in bone. We aimed to investigate the clinicopathological features of this variant across all anatomic sites through a large multi-institutional study.We complied a total of 24 myoepitheliomas with syncytial growth from our files. The tumors occurred in 12 male and 12 female patients (M:F = 1:1), with a median age of 31 years (range, 9-69 years). While the majority of tumors (75%, n = 18) occurred in skin, a significant subset (25%, n = 6) arose in non-cutaneous sites, including bone (n = 3), bronchus/trachea (n = 2), and interosseous membrane of tibia/fibula (n = 1). Tumor size ranged from 0.4 to 5.9 cm. Clinical follow-up (7 patients; range 14-202 months; median 56.5 months) showed a single local recurrence 8 years after incomplete skin excision but no metastases; all patients were alive at the time of last follow-up without evidence of disease. Histologically, all tumors were pink at low-power and characterized by a syncytial growth of bland ovoid, spindled, or histiocytoid cells with eosinophilic cytoplasm and prominent perivascular lymphoplasmacytic inflammation. One-third displayed adipocytic metaplasia (8/24). Rare cytologic atypia was seen but was not associated with increased mitotic activity. All tumors expressed S100, SMA, and/or EMA. Keratin expression was absent in most cases. Molecular analysis was performed in 16 cases, all showing EWSR1-rearrangments. In total, 15/15 (100%) harbored an EWSR1::PBX3 fusion, whereas 1 case EWSR1 FISH was the only molecular study performed.Syncytial myoepithelioma is a rare but recognizable morphologic variant of myoepithelioma which may have a predilection for skin but also occurs in diverse non-cutaneous sites. Our series provides evidence supporting a reappraisal of the term "cutaneous syncytial myoepithelioma," as 25% of patients in our series presented with non-cutaneous tumors; thus, we propose the term "syncytial myoepithelioma" to aid pathologist recognition and avoidance of potentially confusing terminology when referring to non-cutaneous examples. The behavior of syncytial myoepithelioma, whether it arises in cutaneous or non-cutaneous sites, is indolent and perhaps benign with a small capacity for local recurrence.© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.