{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,3]],"date-time":"2026-10-03T16:54:31Z","timestamp":1791046471960,"version":"4.1.0"},"reference-count":41,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2026,8,19]],"date-time":"2026-08-19T00:00:00Z","timestamp":1787097600000},"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. Med."],"abstract":"<jats:p>Extraskeletal osteosarcoma is a rare and aggressive malignant mesenchymal tumor that accounts for approximately 1% of all soft tissue sarcomas and usually arises in the deep soft tissues of the extremities. Primary visceral involvement is extremely uncommon. We report a rare case of primary gastric extraskeletal osteosarcoma in a 65-years-old woman who presented with progressive abdominal pain, distension, nausea, vomiting, and cessation of flatus and defecation. Contrast-enhanced abdominal computed tomography revealed a large cystic-solid mass in the left middle and lower abdomen, with linear calcifications and central non-enhancing areas suggestive of necrosis and cystic degeneration. Because of worsening obstructive symptoms, an emergency radical distal gastrectomy was performed. Histopathological examination showed spindle-shaped tumor cells arranged in sheets, with multifocal lace-like malignant osteoid formation. Immunohistochemical findings, together with exclusion of metastatic skeletal osteosarcoma, supported the diagnosis of primary gastric extraskeletal osteosarcoma. Adjuvant chemotherapy was recommended after surgery, but was declined because of the patient\u2019s poor general condition. No evidence of local recurrence or distant metastasis was observed during 9 months of follow-up. This case highlights that primary gastric extraskeletal osteosarcoma, although extremely rare, should be considered in the differential diagnosis of atypical gastric or intra-abdominal masses with calcification, necrosis, and spindle-cell morphology. Complete surgical resection remains the main treatment, and close long-term surveillance is essential because of the high risk of recurrence and metastasis.<\/jats:p>","DOI":"10.3389\/fmed.2026.1901151","type":"journal-article","created":{"date-parts":[[2026,8,19]],"date-time":"2026-08-19T15:37:23Z","timestamp":1787153843000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":1,"title":["Case Report: Primary gastric extraskeletal osteosarcoma and literature review"],"prefix":"10.3389","volume":"13","author":[{"given":"Xiangrui","family":"Meng","sequence":"first","affiliation":[{"name":"The First Clinical Medical School, Lanzhou University, Lanzhou","place":["Gansu, China"]},{"name":"Department of General Surgery, The First Hospital of Lanzhou University, Lanzhou","place":["Gansu, China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Zheng","family":"Ma","sequence":"additional","affiliation":[{"name":"The First Clinical Medical School, Lanzhou University, Lanzhou","place":["Gansu, China"]},{"name":"Department of General Surgery, The First Hospital of Lanzhou University, Lanzhou","place":["Gansu, China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Zihe","family":"Dong","sequence":"additional","affiliation":[{"name":"The First Clinical Medical School, Lanzhou University, Lanzhou","place":["Gansu, China"]},{"name":"Department of General Surgery, The First Hospital of Lanzhou University, Lanzhou","place":["Gansu, China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jie","family":"Cao","sequence":"additional","affiliation":[{"name":"The First Clinical Medical School, Lanzhou University, Lanzhou","place":["Gansu, China"]},{"name":"Department of Clinical Laboratory, The First Hospital of Lanzhou University, Lanzhou","place":["Gansu, China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yanyan","family":"Lin","sequence":"additional","affiliation":[{"name":"The First Clinical Medical School, Lanzhou University, Lanzhou","place":["Gansu, China"]},{"name":"Department of General Surgery, The First Hospital of Lanzhou University, Lanzhou","place":["Gansu, China"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1965","published-online":{"date-parts":[[2026,8,19]]},"reference":[{"key":"B1","doi-asserted-by":"publisher","first-page":"2126","DOI":"10.1016\/j.radcr.2023.03.009","article-title":"Beyond the bones: extraskeletal osteosarcoma of the thigh.","volume":"18","author":"Shaar","year":"2023","journal-title":"Radiol Case Rep."},{"key":"B2","doi-asserted-by":"publisher","first-page":"332","DOI":"10.1186\/s13256-024-04608-x","article-title":"Extraskeletal osteosarcoma infiltrating pancreas, spleen, gastric, and left kidney: a case report.","volume":"18","author":"Jeo","year":"2024","journal-title":"J Med Case Rep."},{"key":"B3","doi-asserted-by":"publisher","first-page":"e2","DOI":"10.2106\/jbjs.M.00339","article-title":"Analysis of outcomes in extraskeletal osteosarcoma: a review of fifty-three cases.","volume":"96","author":"Choi","year":"2014","journal-title":"J Bone Joint Surg Am."},{"key":"B4","doi-asserted-by":"publisher","first-page":"1359","DOI":"10.1002\/1097-0142(197306)31:6<1359::aid-cncr2820310609>3.0.co;2-f","article-title":"Radiation-induced extraskeletal osteosarcoma.","volume":"31","author":"Alpert","year":"1973","journal-title":"Cancer."},{"key":"B5","doi-asserted-by":"publisher","first-page":"261","DOI":"10.1177\/030089168006600215","article-title":"On radiation-induced extraskeletal osteosarcoma: report of a case.","volume":"66","author":"Ascenzi","year":"1980","journal-title":"Tumori."},{"key":"B6","doi-asserted-by":"publisher","first-page":"115","DOI":"10.3928\/0147-7447-19800201-04","article-title":"Extraosseous osteogenic sarcoma: a clinical analysis of ten cases.","volume":"3","author":"Wu","year":"1980","journal-title":"Orthopedics."},{"key":"B7","doi-asserted-by":"publisher","first-page":"452","DOI":"10.1186\/s12891-020-03429-5","article-title":"Intraperitoneal extraosseous osteosarcoma: a case report and literatures review.","volume":"21","author":"Wang","year":"2020","journal-title":"BMC Musculoskelet Disord."},{"key":"B8","doi-asserted-by":"publisher","first-page":"2036361317749651","DOI":"10.1177\/2036361317749651","article-title":"Extraskeletal osteosarcoma: a large series treated at a single institution.","volume":"10","author":"Wang","year":"2018","journal-title":"Rare Tumors."},{"key":"B9","doi-asserted-by":"publisher","first-page":"393","DOI":"10.1016\/j.prp.2013.03.010","article-title":"Extraskeletal osteosarcoma: a very rare case report of primary tumor of the colon-rectum and review of the literature.","volume":"209","author":"Iannaci","year":"2013","journal-title":"Pathol Res Pract."},{"key":"B10","doi-asserted-by":"publisher","first-page":"1009","DOI":"10.2147\/rmhp.S296172","article-title":"Primary exophytic extraskeletal osteosarcoma of the liver: a case report and literature review.","volume":"14","author":"Zhang","year":"2021","journal-title":"Risk Manag Healthc Policy."},{"key":"B11","doi-asserted-by":"publisher","first-page":"430","DOI":"10.1007\/s00270-009-9575-x","article-title":"Retroperitoneal extraskeletal osteosarcoma: imaging findings and transarterial chemoembolization.","volume":"33","author":"Zhang","year":"2010","journal-title":"Cardiovasc Intervent Radiol."},{"key":"B12","doi-asserted-by":"publisher","first-page":"1364937","DOI":"10.3389\/fmed.2024.1364937","article-title":"Case report: a 17-year-old male with primary pulmonary osteosarcoma.","volume":"11","author":"Wen","year":"2024","journal-title":"Front Med (Lausanne)."},{"key":"B13","doi-asserted-by":"publisher","first-page":"5339","DOI":"10.1002\/cncr.24566","article-title":"Addition of muramyl tripeptide to chemotherapy for patients with newly diagnosed metastatic osteosarcoma: a report from the Children\u2019s Oncology Group.","volume":"115","author":"Chou","year":"2009","journal-title":"Cancer."},{"key":"B14","doi-asserted-by":"publisher","first-page":"776","DOI":"10.1200\/jco.2002.20.3.776","article-title":"Prognostic factors in high-grade osteosarcoma of the extremities or trunk: an analysis of 1,702 patients treated on neoadjuvant cooperative osteosarcoma study group protocols.","volume":"20","author":"Bielack","year":"2002","journal-title":"J Clin Oncol."},{"key":"B15","doi-asserted-by":"publisher","first-page":"907127","DOI":"10.1155\/2010\/907127","article-title":"Extraosseous osteosarcoma of the esophagus: a case report.","volume":"2010","author":"Wegner","year":"2010","journal-title":"Sarcoma."},{"key":"B16","doi-asserted-by":"publisher","first-page":"31","DOI":"10.4137\/CCRep.S38384","article-title":"Primary hepatic osteosarcoma: a rare cause of primary liver tumor.","volume":"9","author":"Tamang","year":"2016","journal-title":"Clin Med Insights Case Rep."},{"key":"B17","doi-asserted-by":"publisher","first-page":"267","DOI":"10.1186\/s12957-021-02337-9","article-title":"Primary extraskeletal osteosarcoma of sigmoid mesocolon: a case report and a review of the literature.","volume":"19","author":"Nie","year":"2021","journal-title":"World J Surg Oncol."},{"key":"B18","doi-asserted-by":"publisher","first-page":"473","DOI":"10.1016\/j.prp.2007.03.005","article-title":"Extraosseous osteosarcoma arising from the small intestinal mesentery.","volume":"203","author":"Heukamp","year":"2007","journal-title":"Pathol Res Pract."},{"key":"B19","doi-asserted-by":"publisher","first-page":"650","DOI":"10.1097\/rlu.0000000000001210","article-title":"Extraosseous osteosarcoma of the liver demonstrated on 18F-FDG PET\/CT imaging.","volume":"41","author":"Jiang","year":"2016","journal-title":"Clin Nucl Med."},{"key":"B20","doi-asserted-by":"publisher","first-page":"85","DOI":"10.1016\/s0046-8177(86)80159-9","article-title":"Extraosseous osteosarcoma presenting with intestinal hemorrhage: case report and literature review.","volume":"17","author":"Nojima","year":"1986","journal-title":"Hum Pathol."},{"key":"B21","doi-asserted-by":"publisher","first-page":"424","DOI":"10.4103\/0973-1482.103524","article-title":"Extra osseous osteosarcoma of the retroperitoneum: an unusual entity.","volume":"8","author":"Ratnagiri","year":"2012","journal-title":"J Cancer Res Therap."},{"key":"B22","doi-asserted-by":"publisher","first-page":"412","DOI":"10.1055\/s-0043-1764144","article-title":"Paratesticular osteosarcoma-a rare tumor with distinctive imaging findings.","volume":"33","author":"Nithiyanandham","year":"2023","journal-title":"Indian J Radiol Imaging."},{"key":"B23","doi-asserted-by":"publisher","first-page":"464","DOI":"10.1007\/s13193-016-0542-0","article-title":"Large retroperitoneal extraosseous osteosarcoma invading into the spine: a case report.","volume":"7","author":"Nagpal","year":"2016","journal-title":"Indian J Surg Oncol."},{"key":"B24","doi-asserted-by":"publisher","first-page":"239","DOI":"10.1017\/s0022215100099059","article-title":"Extraosseous osteogenic sarcoma of the parotid gland.","volume":"100","author":"Manning","year":"1986","journal-title":"J Laryngol Otol."},{"key":"B25","doi-asserted-by":"publisher","first-page":"333","DOI":"10.1016\/j.anl.2011.07.014","article-title":"Extraosseous osteosarcoma in the neck.","volume":"39","author":"Luna-Ortiz","year":"2012","journal-title":"Auris Nasus Larynx."},{"key":"B26","doi-asserted-by":"publisher","first-page":"1549722","DOI":"10.3389\/fonc.2025.1549722","article-title":"The resection of extraosseous osteosarcoma was accompanied by the occurrence of pulmonary metastasis and distal metastasis at the primary site: a case report.","volume":"15","author":"Liu","year":"2025","journal-title":"Front Oncol."},{"key":"B27","doi-asserted-by":"publisher","first-page":"e56050","DOI":"10.7759\/cureus.56050","article-title":"Penile osteosarcoma: a rare extraosseous site.","volume":"16","author":"Khanna","year":"2024","journal-title":"Cureus."},{"key":"B28","doi-asserted-by":"publisher","first-page":"507","DOI":"10.5980\/jpnjurol1989.88.507","article-title":"[A case of primary osteogenic sarcoma of the kidney].","volume":"88","author":"Ito","year":"1997","journal-title":"Nihon Hinyokika Gakkai Zasshi."},{"key":"B29","first-page":"7929","article-title":"Primary renal extra-osseous osteosarcoma.","volume":"22","author":"Flynn","year":"2015","journal-title":"Can J Urol."},{"key":"B30","doi-asserted-by":"publisher","first-page":"111828","DOI":"10.1016\/j.ijscr.2025.111828","article-title":"Incidental primary renal extraosseous osteosarcoma: a case report.","volume":"135","author":"Do","year":"2025","journal-title":"Int J Surg Case Rep."},{"key":"B31","doi-asserted-by":"publisher","first-page":"1215","DOI":"10.1007\/s12070-023-03497-8","article-title":"A rare case of extraosseous osteosarcoma (EOS) of parotid gland.","volume":"75","author":"Dabas","year":"2023","journal-title":"Indian J Otolaryngol Head Neck Surg."},{"key":"B32","doi-asserted-by":"publisher","first-page":"11","DOI":"10.2147\/imcrj.S233674","article-title":"Primary osteosarcoma of the breast with extensive chondroid matrix in a teenager female patient: the paradoxical diagnosis in breast mastopathy.","volume":"13","author":"Yahaya","year":"2020","journal-title":"Int Med Case Reports J."},{"key":"B33","doi-asserted-by":"publisher","first-page":"504","DOI":"10.1097\/MAJ.0b013e3182436afd","article-title":"Primary osteosarcoma of the ureter.","volume":"343","author":"Zhang","year":"2012","journal-title":"Am J Med Sci."},{"key":"B34","doi-asserted-by":"publisher","first-page":"73","DOI":"10.1097\/00043426-200301000-00015","article-title":"A chemosensitive pediatric extraosseous osteosarcoma: case report and review of the literature.","volume":"25","author":"Wodowski","year":"2003","journal-title":"J Pediat Hematol Oncol."},{"key":"B35","doi-asserted-by":"publisher","first-page":"5185604","DOI":"10.1155\/2018\/5185604","article-title":"Rare extraskeletal osteosarcoma appearing after 55 years on a large stage 3 burn scar.","volume":"2018","author":"Vanhooteghem","year":"2018","journal-title":"Case Rep Dermatol Med."},{"key":"B36","doi-asserted-by":"publisher","first-page":"367","DOI":"10.1007\/bf00182646","article-title":"Extraosseous sarcoma. A case report.","volume":"14","author":"Vaquero","year":"1990","journal-title":"Int Orthop."},{"key":"B37","doi-asserted-by":"publisher","first-page":"913","DOI":"10.1055\/s-2006-925096","article-title":"[Extraosseous osteosarcoma of the thyroid gland].","volume":"85","author":"Hertel","year":"2006","journal-title":"Laryngo Rhino Otol."},{"key":"B38","doi-asserted-by":"publisher","first-page":"191","DOI":"10.3109\/02841868609136403","article-title":"Primary extraosseous osteogenic sarcoma in the retroperitoneal space. A case report and review of the literature.","volume":"25","author":"Skensved","year":"1986","journal-title":"Acta Radiol Oncol."},{"key":"B39","doi-asserted-by":"publisher","first-page":"102","DOI":"10.4103\/0970-1591.94969","article-title":"A case of primary extraosseous penile osteosarcoma and review of the literature.","volume":"28","author":"Shringarpure","year":"2012","journal-title":"Indian J Urol."},{"key":"B40","doi-asserted-by":"publisher","first-page":"e55","DOI":"10.1016\/j.spinee.2013.01.051","article-title":"A case of intradural osteosarcoma of the spine.","volume":"13","author":"Schiller","year":"2013","journal-title":"Spine J."},{"key":"B41","doi-asserted-by":"publisher","first-page":"114","DOI":"10.3109\/02841860902953864","article-title":"Primary extraosseous osteosarcoma of the lung.","volume":"49","author":"Karfis","year":"2010","journal-title":"Acta Oncol (Stockholm, Sweden)."}],"container-title":["Frontiers in Medicine"],"original-title":[],"link":[{"URL":"https:\/\/www.frontiersin.org\/articles\/10.3389\/fmed.2026.1901151\/full","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,8,19]],"date-time":"2026-08-19T15:37:25Z","timestamp":1787153845000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.frontiersin.org\/articles\/10.3389\/fmed.2026.1901151\/full"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,8,19]]},"references-count":41,"alternative-id":["10.3389\/fmed.2026.1901151"],"URL":"https:\/\/doi.org\/10.3389\/fmed.2026.1901151","relation":{},"ISSN":["2296-858X"],"issn-type":[{"value":"2296-858X","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,8,19]]},"article-number":"1901151"}}