BACKGROUND: Extraskeletal osteosarcoma is an extremely rare malignancy that accounts for 1% of soft tissue sarcoma and 4.3% of all osteosarcoma. Extraskeletal osteosarcoma can develop in a patient between the ages of 48 and 60 years. The incidence of extraskeletal osteosarcoma is slightly higher in male patients than in females.
METHODS: A 50-year-old Caucasian male patient presented with a 6-month history of intermittent lower-left back pain that limits his activity. Prior ultrasonography and abdominal computed tomography scan showed a diagnosis of kidney stone and tumor in the lower-left abdomen. The computed tomography urography with contrast revealed a mass suspected as a left retroperitoneal malignant tumor. Hence, the tumor was resected through laparotomy and the patient continued with histopathological and immunohistochemistry examination with the result of extraskeletal osteosarcoma.
CONCLUSIONS: Extraskeletal osteosarcoma presents diagnostic challenges requiring multimodal examination, including histological and immunohistochemistry analyses. This case underscores the aggressive nature and poor prognosis despite undergoing the current suggested treatment.

The objective of the present case series was to investigate the various computed tomography findings of six dogs diagnosed with extraskeletal osteosarcoma (exOSA) at several locations. Among the tumors evaluated, four were subcutaneous, one was mammary, and one involved the intestinal tract. Intralesional mineralization was observed in all six dogs. Most of the tumors were moderately calcified, exhibited amorphous mineralization, and were heterogeneous on post-contrast imaging. Three of the tumors were peripherally enhanced, and regional lymphadenopathy was identified in two of the dogs, which was presumed to be metastatic. No lymph node calcification was reported. Although the presence of intralesional mineralization is not a pathognomonic finding, it was consistently identified in the present case series. Therefore, exOSA should be considered in the differential diagnosis when mineralization occurs in a mass unrelated to osseous structures.

Osteosarcomas occurring in the extraskeletal system are known as extraskeletal osteosarcomas (ESOS). They are rare, highly malignant tumors, associated with poor prognosis Di et al. World J Clin Cases 11(3):662-668 (2023). This is a case report of a gentleman nearing 60s with a liver mass with impending rupture. He underwent resection of the liver mass and was diagnosed to have with ESOS. He underwent a right hepatectomy on an urgent basis. He had an uneventful postoperative recovery. The histopathology report showed a poorly differentiated malignant neoplasm consistent with osteosarcoma. The patient is doing well 75 days after discharge and currently receiving adjuvant chemotherapy with ifosfamide, adriamycin, and cisplatin. We have also done a comprehensive literature review of this rare tumor. It is an elusive disease that is difficult to diagnose radiologically. The treatment includes a combination of surgery and adjuvant treatment.

Extraskeletal osteosarcoma (EOS) is a malignant tumor producing bone matrix and/or chondroid material, without direct attachment to bone or periosteum. In humans and dogs, EOS is highly infiltrating, rapidly growing, often characterized by osteoid deposition and variable ossification, similar to primary skeletal osteosarcoma (SOS). In dogs, EOS arises from visceral and soft tissue locations, occasionally in trauma or foreign body sites, or in granulomas. Few data are currently available on the phenotype of these tumors. The present study aims to assess the expression RUNX2 and Karyopherin alpha-2 in EOS, comparing it with SOS and the data available from the human counterpart. Seventeen cases of canine osteosarcoma (13 EOS and 4 SOS) were retrospectively selected and submitted to immunohistochemistry for RUNX2 and Karyopherin alpha-2. Our results showed that, in EOS, RUNX2 is expressed in a mean of 73.07 ± 5.36 neoplastic cell nuclei, in face of a mean 36.15 ± 6.25 of Karyopherin alpha-2 positive nuclei. Osteoclasts, when present, were negative for both markers. No correlation was observed among the two markers (p > 0.05), nor statistically significant difference in quantitative expression was assessed comparing EOS and SOS groups. RUNX2 is expressed in canine EOS similarly to SOS and could be used as a diagnostic marker in a larger panel. Karyopherin alpha-2 is expressed in canine EOS and SOS similarly to human SOS and could be validated in future studies as an additional diagnostic marker. Further studies should be planned to evaluate the expression of these proteins as prognostic predictive parameters.

OBJECTIVE: The aim of this study was to investigate the clinical, imaging and pathological features of extraskeletal osteosarcoma (EOS) and to improve the understanding of this disease and other similar lesions.
METHODS: The data for 11 patients with pathologically confirmed extraosseous osteosarcoma, including tumour site and size and imaging and clinical manifestations, were analysed retrospectively.
RESULTS: Six patients were male (60%), and 5 were female (40%); patient age ranged from 23 to 76 years (average age 47.1 years). Among the 11 patients, 7 had clear calcifications or ossification with different morphologies, and 2 patients showed a massive mature bone tumour. MRI showed a mixed-signal mass with slightly longer T1 and T2 signals in the tumour parenchyma. Enhanced CT and MRI scans showed enhancement in the parenchyma. Ten patients had different degrees of necrosis and cystic degeneration in the mass, 2 of whom were complicated with haemorrhage, and MRI showed \"fluid‒fluid level\" signs. Of the 11 patients, five patients survived after surgery, and no obvious recurrence or metastasis was found on imaging examination. One patient died of lung metastasis after surgery, and 2 patients with open biopsy died of disease progression. One patient died of respiratory failure 2 months after operation. 2 patients had positive surgical margins, and 1 had lung metastasis 6 months after operation and died 19 months after operation. Another patient had recurrence 2 months after surgery.
CONCLUSIONS: The diagnosis of EOS requires a combination of clinical, imaging and histological examinations. Cystic degeneration and necrosis; mineralization is common, especially thick and lumpy mineralization. Extended resection is still the first choice for localized lesions. For patients with positive surgical margins or metastases, adjuvant chemoradiotherapy is needed.

Extraskeletal osteosarcoma (ESOS) is a rare malignant mesenchymal tumor that originates in the soft tissue. ESOS accounts for less than 1% of all soft tissue sarcomas and exhibits an aggressive behavior with a high propensity for local recurrence and distant metastasis. Despite advances in treatment, the prognosis for ESOS remains poor, with a five-year survival rate of less than 50% and 27% for metastatic patients. Ex vivo models derived from patient samples are critical tools for studying rare diseases with poor prognoses, such as ESOS, and identifying potential new treatment strategies. In this work, we established a novel ESOS ex vivo sarco-sphere model from a metastatic lesion to the dermis for research and functional testing purposes. The ex vivo cell model accurately recapitulated the native tumor, as evidenced by histomorphology and molecular profiles. Through a functional screening approach, we were able to identify novel individual anti-cancer drug sensitivities for different drugs such as romidepsin, miverbresib and to multiple kinase inhibitors. Overall, our new ESOS ex vivo cell model represents a valuable tool for investigating disease mechanisms and answering basic and translational research questions.

A rescued male mixed-breed dog, approximately nine years old, was evaluated due to progressive weight loss and an enlarged abdomen. An ultrasound revealed a large, indeterminate mass with mineral-like margins visible on the radiographs. The animal underwent an exploratory laparotomy, and the mass was excised. Histopathological analysis revealed characteristics consistent with a primary omentum extraskeletal osteosarcoma. This rare neoplasm, originating from mesenchymal cell proliferation and bone matrix production, is highly malignant. It often results in death due to metastasis and local recurrence or necessitates euthanasia post-diagnosis in certain cases.
Um canino macho de aproximadamente 9 anos de idade, sem raça definida, foi recebido para atendimento apresentando sinais de emagrecimento progressivo e aumento de volume abdominal. Um exame ultrassonográfico revelou uma formação de grandes dimensões e de origem indeterminada, apresentando característica de mineralização periférica pela radiografia. Foi realizada laparotomia exploratória com remoção da formação. A análise histopatológica revelou características compatíveis com osteossarcoma primário de omento, uma neoplasia rara originada da proliferação de células mesenquimais com produção de matriz óssea, com alto grau de malignidade, geralmente levando à óbito devido a metástases e recorrência local do tumor ou eutanásia após o diagnóstico em alguns casos.

Extraskeletal osteosarcoma (EOSA) in dogs is a rare malignant mesenchymal tumor of somatic soft tissues or more commonly visceral organs with a poor prognosis. In dogs, EOSAs have been described as arising from multiple locations, but differently from humans, never from a main vessel. In this report, we describe the first case of an EOSA arising from the post-hepatic caudal vena cava in a 7-year-old male neutered mix breed dog. This report focuses on the description of the diagnostic challenges to obtain a preoperative diagnosis, highlights the importance of histopathology for a correct diagnosis, and introduces a new differential diagnosis for an animal presenting with a suspected thrombus of the vena cava.

Extraskeletal osteosarcoma (ESOS) is a malignant tumour developing in soft tissues, characterised by the production of osteoid or bone matrix by tumour cells. The standard treatment for localised ESOS is wide resection. Radiotherapy and chemotherapy are usually incorporated into the management of patients. Two types of chemotherapy regimen are mostly used: an osteosarcoma-type chemotherapy, based on cisplatin, and a soft-tissue sarcoma (STS)-type chemotherapy, using the combination of doxorubicin and ifosfamide. To investigate the difference in survival between these two chemotherapy regimens, a systematic review of studies reporting the 5-year disease-free survival (DFS) rates among patients with ESOS submitted to surgery and who received (neo)adjuvant chemotherapy with osteosarcoma-type or STS-type chemotherapy was carried out.
Of the 401 articles identified by systematically searching the PubMed, Embase and Cochrane Central Register of Controlled Trials databases, six retrospective studies were included in the final analysis. In total, 319 patients with localised/resected ESOS were included in the study.
Our meta-analysis showed a benefit in 5-year DFS favouring the use of osteosarcoma-type chemotherapy (relative risk = 1.32, 95% confidence interval 1.03-1.69; P = 0.54); I2 heterogeneity was 0%. The 5-year DFS rate was 56.3% (95% confidence interval 48.3-64.3) with osteosarcoma-type chemotherapy and 45.2% (95% confidence interval 34.5-55.9) with STS-type chemotherapy, with I2 heterogeneity of 27% and 0%, respectively.
Our analysis suggests that there may be a difference regarding the type of (neo)adjuvant chemotherapy regimen used in the treatment of patients with resected ESOS in favour of osteosarcoma-type chemotherapy. Future studies evaluating the role of this treatment modality in this scenario need to consider the type of chemotherapy regimen when comparing with an arm of surgery with/without radiotherapy alone.

Primary osteosarcoma of the uterus (uOS) is rare, and its standard treatment has not yet been established. Herein, we present the case of a 50-year-old woman with uOS who demonstrated an improved prognosis after multiple surgeries to the metastatic sites. After the initial diagnosis of uOS, the patient showed recurrence and distant metastasis and hence expected to exhibit a poor prognosis. The patient underwent multiple surgical resections of the metastatic as well as primary tumors, which enabled the patient to survive for 24 months after the initial surgery. Considering that the median survival time of patients with uOS is approximately 6 months, the survival rate of our patient is noteworthy. Based on our observations, it is suggested that the resection of the primary and metastatic tumors might contribute to the extension of the survival period of the patient with chemo-resistant uOS.