Dedifferentiated low-grade central osteosarcoma of the proximal tibia: Case report and a brief review of the literature

Dedifferentiated low-grade central osteosarcoma (LGCOS) is an exceptionally rare, biphasic bone neoplasm characterized by the abrupt transition of a low-grade fibroblastic proliferation into a high-grade sarcoma. While conventional LGCOS has a favorable prognosis, dedifferentiation drastically alters the clinical course, presenting significant diagnostic and therapeutic challenges.

We report the case of a 29-year-old male who presented with progressive pain and swelling in the proximal left tibia. Initial radiographs demonstrated an ill-defined lytic lesion, but magnetic resonance imaging revealed a biphasic intramedullary mass with cortical breakthrough. A targeted core needle biopsy confirmed dedifferentiated LGCOS. The patient underwent neoadjuvant chemotherapy, achieving a suboptimal histological response (65% necrosis), followed by wide surgical resection and endoprosthetic reconstruction. Molecular analysis confirmed amplification of MDM2 and CDK4 in both tumor components. Despite adjuvant chemotherapy, the patient developed local recurrence and pulmonary metastases 18 months post-treatment, necessitating revision surgery and metastasectomy. He remains disease-free for three years following salvage therapy.

This case underscores the critical importance of advanced imaging and targeted biopsy in identifying dedifferentiated LGCOS. Furthermore, it highlights the relative chemoresistance of the high-grade component, emphasizing the need for rigorous long-term surveillance and the potential future role of targeted molecular therapies.