Cemento-ossifying fibroma (COF) is classified as a fibro-osseous lesion and usually presents as a progressively growing lesion that can reach a large size if left untreated. Fibrous dysplasia (FD) is a non-neoplastic development that affects the craniofacial bones and is characterized by painless hypertrophy due to the replacement of bone by abnormal fibrous tissue. Herein, a case of concurrent occurrence of COF and FD involving the right mandible is described in a 14-year-old male patient. In this review, the current knowledge of FD and COF is summarized, emphasizing the importance of integrating the understanding of clinical, radiographic, and histopathological features. In addition, the relevant aspects associated with differential diagnosis and patient care are evaluated.

Sarcomatous transformation of fibrous dysplasia (FD) is rare and can occur in patients with McCune-Albright syndrome (MAS). To date, there have been several cases of malignant transformation of FD in the craniofacial area of patients with MAS. Here, we report an additional case of secondary osteosarcoma arising from FD in the mandible of a 41-year-old woman with MAS. The patient complained of rapid swelling in the right facial area, which was initially misdiagnosed as soft tissue sarcoma at another hospital. After neoadjuvant concurrent chemoradiotherapy resulting in poor response, the lesion was surgically resected in our hospital, and the final diagnosis of secondary osteosarcoma was rendered. Currently, post-operative adjuvant chemotherapy is in progress. As a result of our review of 17 reported cases showing malignant transformation in FD/MAS, the M/F ratio was 1:1.1, and the median age at onset of malignancy was 28.6 years. The most commonly affected site was the craniofacial bones (n=13; 76%), and the most common histopathologic type of malignancy was osteosarcoma (n=14; 82%). More than half of the patients (8/15; 53.3%) died within 1 year, mainly due to lung metastasis (6/8; 75%). Taken together, since MAS patients with malignant transformation of FD have a relatively poor prognosis, accurate diagnosis based on histopathologic findings as well as clinical and radiographic information is important to select optimal treatment.