Acral soft tissue tumors are common neoplasms, a subset of which pose a diagnostic challenge. We report 10 cases of a previously unrecognized acral benign soft tissue tumor. These tumors arose on the fingers and toes and involved bone in half of cases. Histologically, the tumors were lobulated and displayed an abundant stroma made of variable fibrous, chondroid and myxoid material reminiscent of cartilaginous or myoepithelial differentiation. Tumor cells harbored small round to reniform nuclei with clear chromatin and inconspicuous nucleoli along with scant eosinophilic cytoplasm. The cells were mostly arranged haphazardly in the stroma but also in small clusters. No mitotic activity was detected. No specific feature was identified in recurrent cases. By immunohistochemistry, the cells consistently stained for CD34 (10/10), ERG (9/10), and SOX9 (7/10). Whole RNA sequencing identified a previously undescribed recurrent in frame THBS1-ADGRF5 gene fusion in all cases. The transcript was confirmed by RT-PCR and was not found in the control group of mimickers including soft tissue chondromas. We propose the name of Acral FibroChondroMyxoid Tumors for this new entity.

中文翻译：

---

新肿瘤亚型“肢端纤维软骨粘液样肿瘤”中复发的新型 THBS1-ADGRF5 基因融合。

肢端软组织肿瘤是常见的肿瘤，其中一部分对诊断提出了挑战。我们报告了 10 例以前未被识别的肢端良性软组织肿瘤。这些肿瘤出现在手指和脚趾上，半数病例累及骨骼。组织学上，肿瘤呈分叶状，显示出丰富的间质，间质由可变的纤维、软骨样和粘液样物质组成，让人联想到软骨或肌上皮分化。肿瘤细胞具有小的圆形至肾形细胞核，染色质清晰，核仁不明显，胞质嗜酸性。细胞大多随意排列在基质中，但也有小簇排列。未检测到有丝分裂活动。在复发病例中未发现具体特征。通过免疫组织化学，细胞一致染色 CD34 (10/10)、ERG (9/10)、和 SOX9 (7/10)。在所有病例中，全 RNA 测序鉴定出先前未描述的框架内复发 THBS1-ADGRF5 基因融合。该转录物通过 RT-PCR 得到证实，并且在包括软组织软骨瘤在内的对照组中未发现。我们建议将这个新实体命名为 Acral FibroChondroMyxoid Tumors。