High-grade osteosarcoma as a second primary neoplasm after breast cancer: diagnostic challenge of a thoracic mass

Abstract

Introduction: High-grade surface osteosarcoma is a rare and aggressive bone malignancy. The occurrence of osteosarcoma as a second primary tumor in patients with a history of breast carcinoma is extremely uncommon and represents a diagnostic challenge, particularly when presenting as a thoracic mass initially suspected of metastasis. Case report: A 73-year-old woman with a history of breast carcinoma treated 15 years earlier presented with dyspnea and right pleural effusion. Computed tomography revealed a chest wall mass involving multiple ribs with pleural extension. Histopathology showed a malignant spindle-cell neoplasm with osteoid formation. Immunohistochemistry was positive for SATB2 and CD99 and negative for epithelial markers, confirming high-grade osteosarcoma. PET-CT demonstrated disseminated pulmonary and bone metastases. Multidisciplinary palliative management was established. Results: Morphological and immunohistochemical correlation allowed exclusion of metastatic breast carcinoma and confirmed high-grade osteosarcoma as a second primary malignancy diagnosed at an advanced stage. Conclusions: Osteosarcoma should be included in the differential diagnosis of new thoracic masses in patients with prior malignancy. Immunohistochemistry, particularly SATB2 expression, is essential for diagnosis. Multidisciplinary evaluation is crucial in advanced disease.