Abstract
Background: Fibrous dysplasia and Simple bone cyst are all common benign lesions. A case of osteosarcoma developing from fibrous dysplasia in combination with unicameral bone cyst will be discussed. The radiologic, histologic characteristics and clinical prognostic of the patient will be described. As far as we know, this is the first case report of malignant transformation secondary to fibrous dysplasia in combination with unicameral bone cyst, which is extremely rare and worthy of clinical attention or vigilance. Case presentation: This study describes a case of a 20-years-old male who suffered a 7-years history of intermittent pain in his right proximal tibia, obvious after activity and progressively worsening. Clinical symptoms and imaging examination were consistent with the characteristics of benign primary bone tumor. He underwent a successful curettage operation. Pathological diagnosis was fibrous dysplasia in combination with unicameral bone cyst. After the curettage surgery, the pain in his right knee quickly disappeared and function activities returned to normal during a regular follow-up postoperative. However, He was diagnosed with a recurrence of fibrous dysplasia in combination with unicameral bone cyst and osteosarcoma malignant transformation by chief complaint symptoms of pain and swelling in the right proximal tibia, adequate imaging examination, and pathological diagnosis at 2 years follow-up. Then the patient undergo a limb salvage with tumor prosthesis reconstruction of the right knee. Unfortunately, multiple and unresectable lymph nodes distant metastases happened even with two weeks localized inguinal radiotherapy treatment and one course of neoadjuvant chemotherapy monthly. He eventually received cancer hospice care and died eight months after the diagnosis as malignant transformation and systemic multiple organ metastasis.Conclusions: Although malignant transformation of fibrous dysplasia in combination with unicameral bone cyst is very rare, patients with this disease should be monitored and received lifelong follow-up to obtain early detection, diagnosis and treatment to maximize the efficacy of treatment and survival time. The histological and immunohistochemical findings is very important but not enough. Further research is required to clarify the pathogenesis and prevent malignant transformation.