Chondroblastic Osteosarcoma of the Mandible in a Patient on Risedronate: A Rare Case of Neoadjuvant Chemotherapy Failure.

Osteosarcoma of the jaw only represents 0.5-1% of tumors of the facial mass. Due to its rarity, clinical diagnosis is thus difficult. The guidelines for this pathology remain unclear, and the need for neoadjuvant chemotherapy is still debated. This case report aims to describe a rare case of chondroblastic osteosarcoma in a 50-year-old woman on risedronate treated by neoadjuvant chemotherapy. The tumor extended from the mandibular left first premolar to the mandibular right canine. An excisional biopsy was performed, leading to a diagnosis of chondroblastic osteosarcoma. Neoadjuvant chemotherapy was ineffective, as it did not result in the shrinkage of the tumor. A pelvi-mandibulectomy with fibula free flap reconstruction of the mandible was subsequently successfully performed followed by radiotherapy.