The resection of extraosseous osteosarcoma was accompanied by the occurrence of pulmonary metastasis and distal metastasis at the primary site: a case report - Liu, Han; Tian, Leilei; Mu, Jianhua; He, Xuanhong; Zhuangzhuang, Li; Gong, Taojun; Wang, Jingjing; Min, Li; Lu, Minxun; Tu, Chongqi (Frontiers in Oncology, 2025)