RESUMO
BACKGROUND: McCune-Albright syndrome is a relatively rare disease characterized by the trio of fibrous dysplasia, café-au-lait pigmentation, and endocrine disturbances. It predominantly affects females and may be associated with sarcomatous degeneration in 0.4% to 4% of the cases. CASE REPORT: This article reports on the case of a 24-year-old female patient who had presented a mass in the oral cavity for 30 days, probably originating from the left ramus of the mandible. She had a previous diagnosis of polyostotic fibrous dysplasia, along with café-au-lait spots and endocrine disorders, thus characterizing McCune-Albright syndrome. Histopathological examination of a biopsy specimen revealed osteosarcoma of the mandible. The patient underwent chemotherapy and a surgical procedure for lesion resection. One year has now passed since the patient's operation, and the disease is under control. DISCUSSION: The patient presented sarcomatous degeneration in areas of fibrous dysplasia, consisting of mesenchymal cells that produced osteoid. Malignant degeneration is rare when it is not associated with McCune-Albright syndrome. There is no curative treatment for the syndrome. Attending physicians need to bring endocrine disorders under control, with surgical treatment in cases of significant deformities, as well as providing clinical and psychological care.