A Rare Pediatric Example of Subcutaneous Extraskeletal Osteosarcoma: A Case Report and Review of the Morphologic Differential Diagnosis

Primary cutaneous extraskeletal osteosarcoma: a series of 16 cases

Extraskeletal osteosarcoma (EOS) is a high grade soft tissue tumour characterised by the production of malignant osteoid, without attachment/involvement of underlying bone/periosteum. Rarely, EOS presents as a cutaneous tumour. The clinical behaviour of primary cutaneous EOS (PC-EOS) remains incompletely characterised. Herein we present the largest case series of PC-EOS reported to date. Sixteen PC-EOS cases from the archives/consultation files were retrieved (male:female 1:1; age 31-96 years, mean age 66 years). The tumours measured 1-10 cm (mean 3.2 cm) and were located on the lower extremity (7), head (6), upper extremity (2), and trunk (1). They consisted of pleomorphic, spindled-to-epithelioid cells, with fascicular, nodular, or sheet-like growth patterns and foci of malignant osteoid. Immunohistochemistry did not reveal specific lines of differentiation, and there was no evidence of other tumour types. A literature review was conducted to identify all well characterised cases of PC-EOS. A combined analysis of present and past cases was performed to determine overall trends in clinical characteristics and outcomes. The mean follow-up period was 23.9 months, during which 67.5% of patients experienced progression-free survival and 18% of patients died of disease. Rates of local recurrence and metastasis were 10% and 25%, respectively, approximately double past estimates. These data suggest that the prognosis of PC-EOS is less favourable than previously thought. The differential diagnosis includes benign entities (e.g., ossifying pyogenic granuloma) and malignant neoplasms with heterologous osteosarcomatous differentiation (e.g., carcinosarcoma, transdifferentiated melanoma). Wide excision remains the standard of care, and the role of chemotherapy and radiation remains inconclusive. Recognition of this rare entity can facilitate prompt diagnosis and appropriate treatment.

Immunophenotyping of an Unusual Mixed-Type Extraskeletal Osteosarcoma in a Dog

A 6-year-old female Maltese dog presented with a cervical mass without pain. The tumor was surrounded by a thick fibrous tissue and consisted of an osteoid matrix with osteoblasts and two distinct areas: a mesenchymal cell-rich lesion with numerous multinucleated giant cells and a chondroid matrix-rich lesion. The tumor cells exhibited heterogeneous protein expression, including a positive expression of vimentin, cytokeratin, RANKL, CRLR, SOX9, and collagen 2, and was diagnosed as extraskeletal osteosarcoma. Despite its malignancy, the dog showed no sign of recurrence or metastasis three months after the resection. Further analysis of the tumor cells revealed a high expression of proliferation- and metastasis-related biomarkers in the absence of angiogenesis-related biomarkers, suggesting that the lack of angiogenesis and the elevated tumor-associated fibrosis resulted in a hypoxic tumor microenvironment and prevented metastasis.

Extraskeletal osteosarcoma arising in the subcutaneous tissue of the lower leg: A case report and literature review

Extraskeletal osteosarcoma (ESOS) is a rare soft tissue sarcoma accounting for 1-2% of all soft tissue sarcomas. ESOS originating in the superficial (cutaneous-subcutaneous) tissue is extremely rare, and only 17 cases with subcutaneous ESOS have been reported in detail to date. The aim of the present study was to report an additional case of subcutaneous ESOS of the lower leg and review previous reports of subcutaneous ESOS, focusing on the clinical characteristics, including the MIB-1 labeling index, treatment methods and outcomes. A 79-year-old healthy man presented with a 3-year history of a painful, slowly growing mass in his right lower leg that measured ~5 cm in greatest dimension. Excisional biopsy was performed, and ESOS was diagnosed based on the histopathological findings. A wide resection was performed when local recurrence developed. Six months after the wide resection, lung metastasis was detected. Considering the patient's age, stereotactic radiotherapy was performed without chemotherapy. The patient showed no evidence of local recurrence or new distant metastases for 2 years after the second surgery. We herein present this case of subcutaneous ESOS and review the previous 17 reported cases of subcutaneous ESOS. The 5-year survival rate of patients with subcutaneous ESOS was 78.6%, which was better compared with that of ESOS cases arising in deep soft tissue. Therefore, patients with subcutaneous ESOS may have a better prognosis compared with those with deep-seated ESOS, although the mean MIB-1 labeling index of subcutaneous ESOS was 24%.

Pancreatic Extraskeletal Osteosarcoma Metastasizing to the Scalp

Extraskeletal osteosarcoma (ESOS) is a rare mesenchymal soft-tissue neoplasm that accounts for approximately 1% of all soft-tissue sarcomas. Over 70% of these malignant tumor progress to local recurrence and metastasis. It commonly metastasizes to the lungs, lymph nodes, bone, and skin and has a poor survival outcome. Cutaneous metastasis is exceedingly rare and known to be a sign of widespread metastases. We present a 57-year-old woman who presented with a rapidly growing protuberant mass on the scalp that was finally diagnosed as metastatic ESOS from a primary pancreatic ESOS. To our knowledge, there has been no reported case of pancreatic ESOS metastasizing to the scalp.

Subcutaneous extraskeletal osteosarcoma of the forearm: a case report and review of the literature

Extraskeletal osteosarcoma (ESOS) originating in the subcutaneous tissue is a rare occurrence, accounting for less than 10 % of ESOS cases. Osteosarcoma of extraskeletal origin accounts for approximately 2-4 % of all osteosarcomas, and 1 % of soft tissue sarcomas. We report a case of an 80-year-old female with an isolated primary subcutaneous tumor of the forearm. After imaging, surgical excision, and pathological analysis, the diagnosis of a subcutaneous osteosarcoma was made. This report documents the clinical and pathological findings of subcutaneous ESOS in this case, along with a review of previous cases of subcutaneous ESOS.