A case of secondary chondrosarcoma with TP53 mutation arising from fibrous dysplasia

Malignant transformation in fibrous dysplasia (FD) is a rare event, reported to occur in approximately less than 1% of cases. The most common type of secondary malignant tumor arising from FD is osteosarcoma. We report a case of secondary chondrosarcoma arising in a patient with polyostotic FD. Magnetic resonance imaging (MRI) showed a multilobulated tumor, 12.6 cm in diameter, in the right scapular region. Histologically, the secondary tumor was composed of a proliferation of atypical chondroblasts within chondromatous stroma adjacent to the FD area. Atypical chondroblasts showed pleomorphism and obvious nuclear atypia. Mitotic figures, including atypical ones and focal necrosis were also seen. Based on these findings, we diagnosed chondrosarcoma, Grade 3, arising from FD. Genetic testing revealed a R201H GNAS mutation in both components and a TP53 mutation in the chondrosarcoma area only, suggesting an important role for TP53 mutation in this malignant transformation. The patient remains alive with no evidence of disease recurrence 6 months after surgery.