浅表 CD34 阳性成纤维细胞肿瘤 (SCD34FT) 是一种罕见但独特的皮肤和皮下组织低度肿瘤，免疫组织化学 (IHC) 检测显示 CADM3 频繁表达。在这项研究中，受一个类似“非典型纤维组织细胞瘤 (FH)”且 CADM3 IHC 呈阳性的指示病例的启发，我们通过应用 CADM3 和荧光原位杂交 (FISH) 系统地检查了一组先前诊断为“非典型 FH”的肿瘤检索40例非典型FH，包括CD34阳性肿瘤（n = 20）和CD34阴性肿瘤（n = 20）。所有肿瘤均进行 CADM3 染色。所有 CADM3 阳性肿瘤均通过 FISH 进行评估，以评估 PRDM10 重排。 11 个 CD34 阳性肿瘤（11/20，55%）共表达 CADM3，并被重新分类为 SCD34FT。 CD34 阴性非典型 FH 中没有 (0/20) CADM3 阳性。重新分类的 SCD34FT (10/11) 发生于下肢，经常累及大腿 (n = 8)。在许多重新分类的病例中观察到提示非典型 FH 的特征，包括可变的细胞结构、纺锤形形态、浸润性肿瘤边缘、胶原蛋白滞留、表皮色素沉着和棘皮症。还存在不同程度突出的多核巨细胞，包括 Touton 样形式。在 10/11 重新分类的肿瘤中获得了信息丰富的 FISH 结果，其中 60% (6/10) 表现出 PRDM10 重排。肿瘤组织学上与非典型 FH 相似的一个显着子集，并且 CD34 呈阳性，共表达 CADM3 并带有 PRDM10 重排，支持他们重新分类为 SCD34FT。了解这种形态重叠以及 CADM3 IHC 的应用有助于区分 SCD34FT 和非典型 FH。© 2024 John Wiley

Superficial CD34-positive fibroblastic tumour (SCD34FT) is an uncommon but distinctive low-grade neoplasm of the skin and subcutis that shows frequent CADM3 expression by immunohistochemistry (IHC). In this study, prompted by an index case resembling 'atypical fibrous histiocytoma (FH)' that was positive for CADM3 IHC, we systematically examined a cohort of tumours previously diagnosed as 'atypical FH' by applying CADM3 and fluorescence in situ hybridization (FISH) for PRDM10 rearrangement, to investigate the overlap between these tumour types.Forty cases of atypical FH were retrieved, including CD34-positive tumours (n = 20) and CD34-negative tumours (n = 20). All tumours were stained for CADM3. All CADM3-positive tumours were evaluated by FISH to assess for PRDM10 rearrangement. Eleven CD34-positive tumours (11/20, 55%) coexpressed CADM3 and were reclassified as SCD34FT. None (0/20) of the CD34-negative atypical FH were CADM3-positive. Reclassified SCD34FT (10/11) arose on the lower extremity, with frequent involvement of the thigh (n = 8). Features suggestive of atypical FH were observed in many reclassified cases including variable cellularity, spindled morphology, infiltrative tumour margins, collagen entrapment, epidermal hyperpigmentation, and acanthosis. Variably prominent multinucleate giant cells, including Touton-like forms, were also present. An informative FISH result was obtained in 10/11 reclassified tumours, with 60% (6/10) demonstrating PRDM10 rearrangement.A significant subset of tumours that histologically resemble atypical FH, and are positive for CD34, coexpress CADM3 and harbour PRDM10 rearrangement, supporting their reclassification as SCD34FT. Awareness of this morphologic overlap and the application of CADM3 IHC can aid the distinction between SCD34FT and atypical FH.© 2024 John Wiley & Sons Ltd.