Department of Pathology, Texas Children's Hospital, Houston, TX, USA.
Department of Pathology & Immunology, Baylor College of Medicine, Houston, TX, USA.
Mod Pathol. 2017 Nov;30(11):1577-1588. doi: 10.1038/modpathol.2017.78. Epub 2017 Jul 28.
Nodular fasciitis is a self-limited myofibroblastic lesion that can be misdiagnosed as a sarcoma as a result of its rapid growth, cellularity, and sometimes prominent mitotic activity. A recurrent translocation t(17;22) has been identified in nodular fasciitis, fusing the coding region of USP6 to the promoter region of MYH9, and resulting in increased USP6 expression. A subset of cases show USP6 rearrangement without the typical fusion variants by RT-PCR, or any MYH9 rearrangement by FISH. We sought to further characterize such tumors using molecular diagnostic assays. A novel RT-PCR assay was designed to detect the two known MYH9-USP6 fusion types in formalin-fixed paraffin-embedded and frozen tissue, and a break-apart FISH assay was designed to detect USP6 rearrangement. Twenty-six cases of nodular fasciitis diagnosed between 2002 and 2013 were retrieved from the pathology files of our institutions and were confirmed to be positive by FISH and/or RT-PCR. Seven samples showed USP6 rearrangement by FISH but were negative for MYH9-USP6 fusion by RT-PCR; these cases were subjected to a next-generation sequencing assay utilizing anchored multiplex PCR technology. This assay targets a single partner gene associated with fusions in bone and soft tissue tumors for agnostic detection of gene fusion partners. Novel fusion partners were identified in all seven cases and confirmed by RT-PCR. Structurally, all fusions consisted of the juxtaposition of the entire coding region of USP6 with the promoter of the partner gene, driving increased USP6 expression. This study confirms the neoplastic nature of nodular fasciitis, defines additional pathogenic fusion partners, and adds to the growing body of literature on USP6-associated neoplasia. Given the diagnostic challenges of these tumors, molecular assays can be useful ancillary tools; however, the prevalence of promoter swapping must be recognized when interpreting results.
结节性筋膜炎是一种自限性的肌纤维母细胞病变,由于其快速生长、细胞丰富,有时有明显的有丝分裂活性,可能被误诊为肉瘤。结节性筋膜炎中已鉴定出一种复发性易位 t(17;22),该易位将 USP6 的编码区融合到 MYH9 的启动子区域,导致 USP6 表达增加。一小部分病例通过 RT-PCR 显示 USP6 重排,而没有典型的融合变体,通过 FISH 显示任何 MYH9 重排。我们试图使用分子诊断检测进一步表征此类肿瘤。设计了一种新的 RT-PCR 检测方法,用于检测福尔马林固定石蜡包埋和冷冻组织中的两种已知的 MYH9-USP6 融合类型,设计了一种断裂分离 FISH 检测方法,用于检测 USP6 重排。从我们机构的病理学档案中检索到 26 例 2002 年至 2013 年期间诊断的结节性筋膜炎病例,并通过 FISH 和/或 RT-PCR 证实为阳性。7 例 FISH 显示 USP6 重排,但 RT-PCR 检测 MYH9-USP6 融合为阴性;对这些病例进行了下一代测序检测,利用锚定多重 PCR 技术。该检测针对与骨和软组织肿瘤融合相关的单个伙伴基因,用于基因融合伙伴的盲目检测。在所有 7 例中均鉴定到新的融合伙伴,并通过 RT-PCR 证实。结构上,所有融合均由 USP6 的整个编码区与伙伴基因的启动子并置组成,导致 USP6 表达增加。这项研究证实了结节性筋膜炎的肿瘤性质,定义了额外的致病融合伙伴,并为 USP6 相关肿瘤的不断增加的文献增添了新内容。鉴于这些肿瘤的诊断挑战,分子检测可以作为有用的辅助工具;但是,在解释结果时必须认识到启动子交换的普遍性。
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