Osteosarcomatous Transformation of Long-Standing Fibrous Dysplasia of the Maxilla.

A 53-year-old female with a history of childhood craniofacial fibrous dysplasia presented with several months of right periorbital pain, hyperglobus, and a palpable cheek mass. Imaging suggested malignant transformation of the maxillary tumor, and endoscopic endonasal biopsy confirmed malignant transformation to osteosarcoma. Guanine nucleotide-binding protein, alpha stimulating ( GNAS )-activating mutation confirmed the fibrous dysplasia origin. The patient underwent neoadjuvant chemotherapy, right total maxillectomy and free flap reconstruction, postoperative chemotherapy and radiation, and secondary orbital and facial reconstruction for globe malposition and repair of a postoperative sinocutaneous fistula. The patient remains tumor-free at 20-month follow-up. This case highlights the rare malignant transformation of craniofacial fibrous dysplasia, demonstrates the importance of molecular analysis for confirmation of its etiogenesis, and illustrates the challenges associated with reconstruction of the orbit and maxilla following cancer resection.