Dedifferentiated chondrosarcoma arising in fibrous dysplasia: A case report and review of the current literature

Background: Fibrous dysplasia is an uncommon bone disease that has rare but clear potential for malignant transformation. The frequency is increased in polyostotic forms, McCune-Albright syndrome, Mazabraud's syndrome, and previously irradiated sites. Rapidly progressing pain unrelated to trauma is the most concerning symptom. The early radiological features of sarcomatous transformation are moth-eaten or cystic areas of osteolysis, cortical destruction, and gradual formation of a soft tissue mass. The prognosis is unfavorable as most of the cases are in an advanced stage at the time of diagnosis. Methods: This case was diagnosed at a large cancer center in Florida. Pertinent clinical findings were obtained from chart review and inter-departmental consultation. Results: Histopathological examination revealed dysplastic lamellar bone with no osteoblastic rimming and "Chinese letter" shapes, areas composed of lobulated hyaline cartilage with mild to severe nuclear atypia, and areas of poorly differentiated cells with a spindled appearance, consistent with chondrosarcoma arising within fibrous dysplasia. Conclusions: Sarcomatous transformation of fibrous dysplasia is an uncommon occurrence, yet has significant importance for those with the disease. There may be difficulty with diagnosis given the symptoms and radiologic findings of benign fibrous dysplasia. We report a case of chondrosarcoma rising in fibrous dysplasia and review the current literature. This case is of interest due to the fact that the diagnosis of monostotic fibrous dysplasia was first made at the age of 59 and malignant transformation occurred within a decade with no history of trauma or radiation. This is an excellent example of how a change in symptoms without a history of trauma should be alarming to the clinician and warrants a thorough work-up for malignancy. To the best of our knowledge, this represents the second case of dedifferentiated chondrosarcoma within the English literature.