Atypical nodular fasciitis with a novel PAFAH1B1-USP6 fusion in a 22-month-old boy
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Atypical nodular fasciitis with a novel PAFAH1B1-USP6 fusion in a 22-month-old boy Yan Qiu 1 & Ran Peng 1 & Huijiao Chen 1 & Hua Zhuang 2 & Xin He 1 & Hongying Zhang 1 Received: 26 May 2020 / Revised: 18 October 2020 / Accepted: 30 October 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Nodular fasciitis (NF) rarely occurs in infants aged < 2 years although cranial fasciitis develops predominantly in this age group. Histologically, NF may present high cellularity and brisk mitoses, but atypical forms are generally absent. Here, we report a NF in a 22-month-old Chinese boy. Microscopically, the lesion was manifested as cellular variant of NF. Notably, atypical mitotic figures including multipolar form were identified. Immunohistochemically, the neoplastic cells showed strong positivity for smooth muscle actin. Fluorescence in situ hybridization analysis revealed an unbalanced rearrangement of USP6, along with the USP6 increased copies. Subsequent next-generation sequencing-based technology revealed a novel PAFAH1B1-USP6 fusion gene as well as unusual fusion point on USP6 (exon 9). To the best of our knowledge, this is the only reported case with overt atypical mitosis. This case is also the first published example of genetically confirmed infant NF. Additionally, PAFAH1B1USP6 fusion has never been described in NF. Keywords Nodular fasciitis . Pediatric . Atypical mitoses . PAFAH1B1-USP6 fusion . Unbalanced rearrangement
Introduction Nodular fasciitis (NF) is one of the most common fibroblastic lesions that may be misdiagnosed as sarcomas [1]. As has been reported, NF usually occurs in adults between 20 and 40 years [1]. Microscopically, NF is typically composed of bland myofibroblasts and fibroblasts immersed in a myxoid or fibrous background. The lesion may exhibit high cellularity and frequent mitotic figures, but atypical forms are generally absent [1, 2]. In 2011, Erickson-Johnson et al. demonstrated that this lesion harbored consistent (> 90%) rearrangement of ubiquitin-specific protease 6 (USP6) on 17p13.2 [3]. Therefore, the clonal nature of NF has been widely accepted, and detection of USP6 rearrangement has been advocated as Supplementary Information The online version contains supplementary material available at https://doi.org/10.1007/s00428-02002961-y. * Hongying Zhang [email protected] 1
Department of Pathology, West China Hospital, Sichuan University, Guoxuexiang 37, Chengdu 610041, Sichuan, China
2
Department of Ultrasound, West China Hospital, Sichuan University, Chengdu 610041, Sichuan, China
an invaluable diagnostic tool for distinguishing challenging cases from their histologic mimics. Here, we report a case of pediatric NF with atypical histologic features harboring a novel PAFAH1B1-USP6 fusion along with unbalanced rearrangement and unusual break point of USP6. To the best of our knowledge, the current case is the first lesion showing multipolar mitotic figure among NF cases. Additionally, this is the first published instance of USP6-positive NF i
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