Snapshot An 13-year-old boy presents to his pediatrician for right distal thigh pain. He has been having pain in this area for the past few months, has progressively worsened, and persists in the night. Physical examination is notable for tenderness upon palpation above the right knee. A radiograph of the distal thigh demonstrates a sunburst pattern and Codman triangle. Introduction Overview malignant bone tumor secondary to overproduction of osteoid cells by malignant cells most commonly affecting the metaphysis of bone Epidemiology Incidence bimodal age distribution adolescence and adults > 65 years of age Risk factors Paget disease of the bone prior irradiation or chemotherapy familial retinoblastoma Li-Fraumeni syndrome teriparatide use ETIOLOGY Pathophysiology unclear Associated conditions Paget disease of the bone familial retinoblastoma Li-Fraumeni syndrome Symptoms Symptoms localized pain typically over several months location metaphyseal regions distal femur proximal tibia proximal humerus systemic symptoms are generally absent e.g., weight loss, fever, and nightsweats Physical exam may have a mass at the site of involvement Imaging Radiography indication initial imaging study finding Codman triangle periosteal new bone formation radiodense and radiolucent areas with bone cortex destruction mostly in the metaphyseal region of bone sunburst appearance new bone formation perpendicular to the shaft of the bone MRI indication to determine the extent of disease important to do the involved entire long bone to find any skip lesions Radionuclide bone scan indication to evaluate for metastatic disease Studies Invasive studies open or core biopsy indication used to confirm the diagnosis Histology findings pleomorphic osteoid-producing cells Differential Ewing sarcoma differentiating factors anaplastic small, round, and blue cells with scant cytoplasm typically affects the diaphysis Treatment Treatment consists of surgical resection (even amputation), chemotherapy, and radiation therapy depends on the grade and extent of the disease Complications Metastasis Amputation Prognosis Prognostic variable positive low-grade negative resection margin negative metastasis unresectable or partially resectable large tumor size