汗囊瘤被认为是汗管单位的良性保留囊肿。病变通常位于眶周皮肤；然而，在面部外部位很少观察到具有类似组织病理学特征的病变。在此，我们介绍了四例面部外皮肤部位的汗囊瘤样肿瘤，其中存在 RET 或 ALK 重排。这项研究的特点是一名 67 岁女性患有 10 毫米大小的数字肿瘤（病例 1），一名 62 岁男性患有 8 毫米大小的锁骨肿瘤（病例 2），一名 61 岁男性患有 19 毫米大小的数字肿瘤（病例 3），一名 11 岁女性，患有 10 毫米大小的小腿肿瘤（病例 4）以及 5 例经典眶周汗囊瘤对照病例（病例 5-9） 。在病例1-4中，观察到包含内立方管腺细胞（p63-和SOX10/-）和外扁平肌上皮（p63-和SOX10-）细胞的两细胞层的多囊性肿瘤。内部导管腺肿瘤细胞表现出微乳头状突起和罗马桥结构。没有观察到明显的非典型细胞。通过下一代测序或桑格测序揭示了病例 1 和 3 中的 NCOA4::RET、病例 2 中的 CCDC6::RET 以及病例 4 中的 SLC12A2::ALK。相反，经典汗囊瘤的对照病例（病例 5-9）在肿瘤细胞中未显示囊内增殖、丰富的细胞质、ALK 免疫反应性或 NCOA4::RET 检测。 RET/ALK 重排的汗囊瘤样肿瘤是可以与经典汗囊瘤区别的肿瘤实体。这种 RET/ALK 重排肿瘤是良性的，经常在手指中观察到。未来的研究将建立汗囊瘤样肿瘤的概念、详细的临床病理学特征和遗传变异。版权所有 © 2024 澳大利亚皇家病理学家学院。由 Elsevier B.V. 出版。保留所有权利。

Hidrocystoma is thought to be a benign retention cyst of sweat ductal units. The lesion is usually located in the periorbital skin; however, lesions with similar histopathological features are rarely observed in extra-facial sites. Herein, we present four cases of hidrocystoma-like tumours in extra-facial skin sites that harboured a RET or ALK rearrangement. This study features a 67-year-old female with a 10 mm-sized digital tumour (Case 1), a 62-year-old male with an 8 mm-sized clavicular tumour (Case 2), a 61-year-old male with a 19 mm-sized digital tumour (Case 3), and an 11-year-old female with a 10 mm-size lower leg tumour (Case 4) as well as five control cases (Cases 5-9) of classical periorbital hidrocystoma. In Cases 1-4, multicystic tumours comprising a two-cell layer of inner cuboidal ductoglandular (p63- and SOX10+/-) and outer flat myoepithelial (p63+ and SOX10+) cells were observed. The inner ductoglandular tumour cells exhibited micropapillary projections and Roman bridging structures. No apparent atypical cells were observed. NCOA4::RET in Cases 1 and 3, CCDC6::RET in Case 2, and SLC12A2::ALK in Case 4 were revealed by next-generation sequencing or Sanger sequencing. In contrast, control cases of classical hidrocystoma (Cases 5-9) did not show intracystic proliferation, abundant cytoplasm, ALK immunoreactivity, or NCOA4::RET detection in the tumour cells. RET/ALK-rearranged hidrocystoma-like tumours are tumour entities that can be distinguished from classical hidrocystoma. This RET/ALK-rearranged neoplasm is benign and is frequently observed in the digits. Future studies will establish the concept, detailed clinicopathological characteristics, and genetic variations of hidrocystoma-like tumours.Copyright © 2024 Royal College of Pathologists of Australasia. Published by Elsevier B.V. All rights reserved.