A Rare Presentation of Extraskeletal Osteosarcoma in the Arm

Abstract

Extraskeletal Osteosarcoma (ESOS) is a rare mesenchymal malignancy that commonly manifests in the fifth to seventh decade of life. It occurs frequently in the deep soft tissues of the lower extremities, in particular the thigh. These are aggressive tumours, showing local recurrence, and almost 90% show a distant metastasis in particular to the lung at the time of diagnosis, so it becomes crucial to diagnose these lesions at an early stage. Here, authors report a case of 56-year-old female, who presented with painless swelling of size 2×2 cm in the lateral aspect of the right arm. There was no history of prior trauma. On imaging studies, it was found to be a subcutaneous swelling with calcification and not attached to the nearby bone. Excision biopsy showed a malignant neoplastic lesion with osteoid surrounded by atypical cells with frequent mitosis, and with heterologous bone and cartilage formation. The diagnosis of ESOS was confirmed using special AT-rich sequence-Binding protein 2 (SAT-B2) immunohistochemistry. The case is presented here because of its rarity of occurrence in the arm, size and utilisation of SAT-B2 in confirming the diagnosis.