DOI: https://doi.org/10.36347/sjmcr.2026.v14i11.016

Pages: 2470-2474

Giant cell tumor of bone (GCTB) is an intermediate, locally aggressive primary bone neoplasm that rarely undergoes malignant transformation. Secondary osteosarcoma arising in GCTB is exceptionally uncommon, particularly in the absence of prior radiotherapy. Although the lungs are the most common site of distant metastasis in osteosarcoma, pleural involvement is rare. We report a rare case of a 27-year-old woman with a history of surgically treated GCTB who subsequently developed bilateral pleural lesions diagnosed as metastatic osteosarcoma. The case highlights the diagnostic challenges associated with identifying secondary malignant transformation in a patient with a previous history of conventional GCTB. Correlation of the clinical history, radiological findings, and histopathological features is essential to establish the diagnosis and distinguish malignant transformation from conventional metastatic GCTB and other primary pleural malignancies.