Imada Hiroki, Torigoe Tomoaki, Yazawa Yasuo, Kanno Satoshi, Ichikawa Jiro, Yamaguchi Takehiko, Kawasaki Tomonori
Department of Pathology, Saitama Medical University Saitama Medical Center, Kawagoe, Japan.
Department of Orthopaedic Oncology and Surgery, Saitama Medical University International Medical Center, Hidaka, Japan.
Front Oncol. 2023 Feb 24;13:1024768. doi: 10.3389/fonc.2023.1024768. eCollection 2023.
Extraskeletal osteosarcoma (EO) is a soft tissue sarcoma characterized by the production of bone matrix by neoplastic cells. Benign osteoid in EO, leading to a diagnostic dilemma, is rarely encountered. Herein, for the first time, we present a case with cytogenetically confirmed EO combined with or preceding myositis ossificans (MO). A 21-year-old man had a mildly painful swelling in his left knee. Imaging studies demonstrated a 39-mm mass with peripheral mineralization and cystic change on the posterolateral side of the left fibular head. He was clinically suspected of having either MO or a malignancy, such that wide resection was performed. Macroscopically, the mass was grayish to brown. In the cut section, multiple cystic lesions in addition to solid components were noted. Histopathologically, the solid components demonstrated diffuse proliferation of pleomorphic tumor cells with osteoclast-like giant cells. The malignant tumor cells formed osteoid. In the periphery, the mass was benign, showing mature bone tissue and focally non-malignant woven bone with fibroblasts, compatible with zonation. Fluorescence hybridization (FISH) demonstrated split signals of the gene. These findings suggested EO with preceding MO. Although the pathogenesis remains to be elucidated, the observed rearrangement might contribute to both the diagnosis of EO with preceding MO and an understanding of the underlying histopathology.
骨外骨肉瘤（EO）是一种软组织肉瘤，其特征是肿瘤细胞产生骨基质。EO中良性类骨质很少见，这会导致诊断困境。在此，我们首次报告一例经细胞遗传学证实的EO合并或先于骨化性肌炎（MO）的病例。一名21岁男性左膝出现轻度疼痛性肿胀。影像学检查显示左腓骨头后外侧有一个39毫米的肿块，周边有矿化和囊性改变。临床上怀疑他患有MO或恶性肿瘤，因此进行了广泛切除。大体上，肿块呈灰白色至棕色。在切面中，除实性成分外还可见多个囊性病变。组织病理学上，实性成分显示多形性肿瘤细胞弥漫性增殖，伴有破骨细胞样巨细胞。恶性肿瘤细胞形成类骨质。在周边，肿块为良性，表现为成熟骨组织和局灶性非恶性编织骨，并伴有成纤维细胞，符合分带现象。荧光原位杂交（FISH）显示该基因有分裂信号。这些发现提示为先于MO的EO。尽管发病机制仍有待阐明，但观察到的重排可能有助于诊断先于MO的EO以及理解其潜在的组织病理学。
