{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,8]],"date-time":"2026-10-08T19:11:05Z","timestamp":1791486665095,"version":"4.3.4"},"reference-count":14,"publisher":"Hindawi Limited","license":[{"start":{"date-parts":[[2010,1,1]],"date-time":"2010-01-01T00:00:00Z","timestamp":1262304000000},"content-version":"unspecified","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/3.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Case Reports in Medicine"],"published-print":{"date-parts":[[2010]]},"abstract":"<jats:p>Extraskeletal osteosarcoma is an uncommon high-grade malignant soft tissue sarcoma. Well-differentiated extraskeletal osteosarcoma is thought to have a better prognosis than classical extraskeletal osteosarcoma, but dedifferentiation after recurrence has also been reported. We present a case of a primary retroperitoneal extraskeletal osteosarcoma in a 62-year-old Japanese woman. Abdominal CT revealed a large mass with diffuse calcification in the right retroperitoneal space and tumor resection was performed. The histopathological diagnosis was well-differentiated retroperitoneal extraskeletal osteosarcoma. She was followed up by CT every 6 months without adjuvant radiotherapy and chemotherapy for 31 months until anaplastic high-grade spindle cell sarcoma recurred in the retroperitoneum. Our case is the seventh reported description of well-differentiated extraskeletal sarcoma, and the first to arise in the retroperitoneum and recur as an entirely dedifferentiated spindle cell sarcoma.<\/jats:p>","DOI":"10.1155\/2010\/327591","type":"journal-article","created":{"date-parts":[[2010,3,4]],"date-time":"2010-03-04T10:30:16Z","timestamp":1267698616000},"page":"1-5","source":"Crossref","is-referenced-by-count":13,"title":["Well-Differentiated Extraskeletal Osteosarcoma Arising from the Retroperitoneum That Recurred as Anaplastic Spindle Cell Sarcoma"],"prefix":"10.1155","volume":"2010","author":[{"given":"Hiromasa","family":"Arai","sequence":"first","affiliation":[{"name":"Department of Pulmonary Medicine (Surgery), Yokohama City University Medical Center, 4-57 Urafune-cho, Minami-ku, Yokohama, 232-0024, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yasushi","family":"Rino","sequence":"additional","affiliation":[{"name":"Department of Surgery, Yokohama City University School of Medicine, 3-9 Fukuura, Kanazawa-ku, Yokohama, 236-0004, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Teppei","family":"Nishii","sequence":"additional","affiliation":[{"name":"Department of Pulmonary Medicine (Surgery), Yokohama City University Medical Center, 4-57 Urafune-cho, Minami-ku, Yokohama, 232-0024, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Norio","family":"Yukawa","sequence":"additional","affiliation":[{"name":"Department of Surgery, Yokohama City University School of Medicine, 3-9 Fukuura, Kanazawa-ku, Yokohama, 236-0004, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Nobuyuki","family":"Wada","sequence":"additional","affiliation":[{"name":"Department of Surgery, Yokohama City University School of Medicine, 3-9 Fukuura, Kanazawa-ku, Yokohama, 236-0004, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hisashi","family":"Oshiro","sequence":"additional","affiliation":[{"name":"Department of Pathology, Yokohama City University School of Medicine, 3-9 Fukuura, Kanazawa-ku, Yokohama, 236-0004, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tsuyoshi","family":"Ishida","sequence":"additional","affiliation":[{"name":"Department of Pathology and Laboratory Medicine, Kohnodai Hospital, National Medical Center of Japan, 1-7-1 Kohnodai, Ichikawa, Chiba, 272-8516, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Noboru","family":"Nakaigawa","sequence":"additional","affiliation":[{"name":"Department of Urology, Yokohama City University School of Medicine, 3-9 Fukuura, Kanazawa-ku, Yokohama, 236-0004, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Munetaka","family":"Masuda","sequence":"additional","affiliation":[{"name":"Department of Surgery, Yokohama City 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