Undifferentiated Round Cell Sarcoma With CRTC1::SS18 Fusion: Expanding Clinicopathologic Features of a Rare Translocation Sarcoma With Prominent Desmoplastic Stroma
{"title":"Undifferentiated Round Cell Sarcoma With CRTC1::SS18 Fusion: Expanding Clinicopathologic Features of a Rare Translocation Sarcoma With Prominent Desmoplastic Stroma","authors":"","doi":"10.1016/j.modpat.2024.100555","DOIUrl":null,"url":null,"abstract":"<div><p>Undifferentiated round cell sarcomas (URCS) represent a diverse group of tumors, including conventional Ewing sarcoma, round cell sarcoma with <em>EWSR1/FUS</em>–non-ETS fusions, <em>CIC</em>-rearranged sarcoma, and sarcoma with <em>BCOR</em> alterations. Since 2018, 3 cases of URCS with a novel <em>CRTC1</em>::<em>SS18</em> gene fusion have been reported in the literature. Herein, we report 3 additional cases of <em>CRTC1</em>::<em>SS18</em> sarcoma, thereby doubling the number of described cases and expanding the clinicopathologic features of this rare translocation sarcoma. Together with the previously reported cases, we show that the male-to-female ratio is 1:2 with a median age of 34 years (range, 12-42 years). Tumors occurred primarily in intramuscular locations involving the lower extremity. Histologically, all tumors contained uniform round-to-epithelioid cells with a moderate amount of eosinophilic cytoplasm growing in sheets and nests with prominent desmoplastic stroma reminiscent of desmoplastic small round cell tumor. Immunohistochemical results were nonspecific, demonstrating variable expression of CD99 (patchy), ALK, GATA3, and cyclin D1. RNA sequencing revealed <em>CRTC1</em>::<em>SS18</em> gene fusions in all cases, involving exons 1 to 2 of <em>CRTC1</em> (the 5′ partner gene) on chromosome 19 and either exon 2 or exon 4 of <em>SS18</em> (the 3′ partner gene) on chromosome 18. The clinical course was variable. Although 1 previously reported case demonstrated aggressive behavior with a fatal outcome, 2 others had a relatively indolent course with gradual growth for 6 to 7 years prior to resection. Two cases developed metastatic disease, including 1 case with bilateral lung metastasis and 1 with locoregional spread to a lymph node. By analyzing the clinicopathologic features, we aimed to improve recognition of this rare translocation sarcoma to better understand its biologic potential, optimize patient management, and expand the current classification of URCS.</p></div>","PeriodicalId":18706,"journal":{"name":"Modern Pathology","volume":null,"pages":null},"PeriodicalIF":7.1000,"publicationDate":"2024-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Modern Pathology","FirstCategoryId":"3","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0893395224001352","RegionNum":1,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"PATHOLOGY","Score":null,"Total":0}
引用次数: 0
Abstract
Undifferentiated round cell sarcomas (URCS) represent a diverse group of tumors, including conventional Ewing sarcoma, round cell sarcoma with EWSR1/FUS–non-ETS fusions, CIC-rearranged sarcoma, and sarcoma with BCOR alterations. Since 2018, 3 cases of URCS with a novel CRTC1::SS18 gene fusion have been reported in the literature. Herein, we report 3 additional cases of CRTC1::SS18 sarcoma, thereby doubling the number of described cases and expanding the clinicopathologic features of this rare translocation sarcoma. Together with the previously reported cases, we show that the male-to-female ratio is 1:2 with a median age of 34 years (range, 12-42 years). Tumors occurred primarily in intramuscular locations involving the lower extremity. Histologically, all tumors contained uniform round-to-epithelioid cells with a moderate amount of eosinophilic cytoplasm growing in sheets and nests with prominent desmoplastic stroma reminiscent of desmoplastic small round cell tumor. Immunohistochemical results were nonspecific, demonstrating variable expression of CD99 (patchy), ALK, GATA3, and cyclin D1. RNA sequencing revealed CRTC1::SS18 gene fusions in all cases, involving exons 1 to 2 of CRTC1 (the 5′ partner gene) on chromosome 19 and either exon 2 or exon 4 of SS18 (the 3′ partner gene) on chromosome 18. The clinical course was variable. Although 1 previously reported case demonstrated aggressive behavior with a fatal outcome, 2 others had a relatively indolent course with gradual growth for 6 to 7 years prior to resection. Two cases developed metastatic disease, including 1 case with bilateral lung metastasis and 1 with locoregional spread to a lymph node. By analyzing the clinicopathologic features, we aimed to improve recognition of this rare translocation sarcoma to better understand its biologic potential, optimize patient management, and expand the current classification of URCS.
期刊介绍:
Modern Pathology, an international journal under the ownership of The United States & Canadian Academy of Pathology (USCAP), serves as an authoritative platform for publishing top-tier clinical and translational research studies in pathology.
Original manuscripts are the primary focus of Modern Pathology, complemented by impactful editorials, reviews, and practice guidelines covering all facets of precision diagnostics in human pathology. The journal's scope includes advancements in molecular diagnostics and genomic classifications of diseases, breakthroughs in immune-oncology, computational science, applied bioinformatics, and digital pathology.