{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,3]],"date-time":"2026-03-03T06:00:54Z","timestamp":1772517654816,"version":"3.50.1"},"reference-count":21,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2026,3,3]],"date-time":"2026-03-03T00:00:00Z","timestamp":1772496000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Immunol."],"abstract":"<jats:p>\n                    Primary undifferentiated pleomorphic sarcoma (UPS) of the renal pelvis is an extremely rare and aggressive mesenchymal malignancy. The diagnosis remains challenged, and its clinical characteristics and treatment strategies remain unclear. Urine fluorescence\n                    <jats:italic>in situ<\/jats:italic>\n                    hybridization (FISH) is a highly sensitive tool for detecting urothelial carcinoma (UC), but \u2018false\u2019-positive results can be observed in non-UC malignancies. We present a challenging case of primary UPS of renal pelvis with positive urine FISH and high programmed death receptor ligand 1 (PD-L1) expression, which complicates the initial diagnosis and opens avenues for potential immunotherapy.\n                  <\/jats:p>","DOI":"10.3389\/fimmu.2026.1769769","type":"journal-article","created":{"date-parts":[[2026,3,3]],"date-time":"2026-03-03T05:23:31Z","timestamp":1772515411000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":0,"title":["Case Report: A rare case of primary undifferentiated pleomorphic sarcoma of the renal pelvis with high PD-L1 expression and a misleading positive urine FISH"],"prefix":"10.3389","volume":"17","author":[{"given":"Jiameng","family":"Li","sequence":"first","affiliation":[{"name":"Department of Pathology, Qilu Hospital of Shandong University","place":["Jinan, Shandong, China"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Xiaoyu","family":"Wang","sequence":"additional","affiliation":[{"name":"Department of Pathology, School of Basic Medical Sciences, Shandong University","place":["Jinan, Shandong, China"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Junhui","family":"Zhen","sequence":"additional","affiliation":[{"name":"Department of Pathology, Qilu Hospital of Shandong University","place":["Jinan, Shandong, China"]},{"name":"Department of Pathology, School of Basic Medical Sciences, Shandong University","place":["Jinan, Shandong, China"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Mei","family":"Qi","sequence":"additional","affiliation":[{"name":"Department of Pathology, Qilu Hospital of Shandong University","place":["Jinan, Shandong, China"]}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1965","published-online":{"date-parts":[[2026,3,3]]},"reference":[{"key":"B1","doi-asserted-by":"publisher","DOI":"10.1016\/j.eucr.2018.01.002","article-title":"Pleomorphic undifferentiated sarcoma: A case of a giant renal mass","volume":"17","author":"\u00c7ilesiz","year":"2018","journal-title":"Urol Case Rep"},{"key":"B2","volume-title":"WHO classification of tumours. 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