Oncology · Bone Tumors
The facts most likely to be tested
Osteosarcoma is the most common primary malignant bone tumor in children and adolescents, typically occurring in the metaphysis of long bones.
The classic radiographic appearance is a sunburst pattern of periosteal reaction and Codman triangle due to elevation of the periosteum.
Patients frequently present with localized bone pain that is often worse at night and may be associated with a palpable soft tissue mass.
Bimodal age distribution peaks in adolescents (associated with rapid bone growth) and elderly adults (often secondary to Paget disease of bone).
Genetic predisposition is a key risk factor, specifically mutations in the RB1 gene (hereditary retinoblastoma) and TP53 gene (Li-Fraumeni syndrome).
Laboratory findings often reveal elevated alkaline phosphatase and lactate dehydrogenase (LDH), which correlate with tumor burden and prognosis.
The definitive management strategy involves neoadjuvant chemotherapy followed by limb-salvage surgery (wide local excision).
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A 15-year-old male presents to the clinic complaining of persistent right knee pain for the past three months. He reports the pain is worse at night and interferes with his sleep. On physical exam, there is a tender, firm mass palpated over the distal femur. Radiographic imaging of the knee reveals a sunburst periosteal reaction and a Codman triangle at the distal femoral metaphysis. Serum labs show an elevated alkaline phosphatase level.
What is the most likely diagnosis?
Osteosarcoma
The patient's age, location of the tumor (metaphysis), and classic radiographic findings of a sunburst pattern and Codman triangle are pathognomonic for osteosarcoma.
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Etiology / Epidemiology
Bimodal distribution: adolescents (10-20y) and elderly (associated with Paget disease of bone).
Clinical Manifestations
Progressive bone pain and swelling; sunburst pattern or Codman triangle on imaging.
Diagnosis
Biopsy is the gold standard; MRI is the preferred modality for local staging.
Treatment
Surgical resection combined with neoadjuvant chemotherapy (methotrexate, doxorubicin, cisplatin).
Prognosis
5-year survival is 60-70% for localized disease; pulmonary metastasis is the primary cause of mortality.
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Epidemiology & Etiology
Most common primary malignant bone tumor in children and adolescents. Bimodal peak occurs in the second decade of life and again in patients >60 years old. Elderly cases are frequently secondary to Paget disease of bone, prior radiation, or bone infarcts.
Pertinent Anatomy
Predominantly affects the metaphysis of long bones, specifically the distal femur, proximal tibia, and proximal humerus. The tumor arises from primitive bone-forming mesenchymal cells, often near the knee joint.
Pathophysiology
Malignant cells produce immature osteoid, leading to rapid bone destruction and reactive periosteal elevation. Genetic predisposition includes Li-Fraumeni syndrome (p53 mutation) and Retinoblastoma (RB1 gene mutation).
Clinical Manifestations
Patients present with localized bone pain that is often worse at night or with activity. Physical exam reveals a palpable, tender mass with limited range of motion at the adjacent joint. Systemic symptoms are rare, but pathologic fractures may be the initial presentation.
Diagnosis
Plain radiographs show the classic sunburst pattern or Codman triangle (periosteal elevation). Biopsy is the definitive diagnostic test. MRI of the entire bone is required to evaluate the extent of marrow involvement and skip lesions.
Treatment
Standard of care is neoadjuvant chemotherapy followed by limb-sparing surgery. First-line agents include methotrexate, doxorubicin, and cisplatin. Amputation is reserved for cases involving neurovascular compromise or extensive soft tissue invasion.
Prognosis
Prognosis depends heavily on the presence of pulmonary metastasis at diagnosis. Patients require serial chest CT scans for surveillance due to the high propensity for lung spread.
Differential Diagnosis
Ewing Sarcoma: onion-skinning periosteal reaction
Osteoid Osteoma: pain relieved by NSAIDs
Osteochondroma: benign, pedunculated bony stalk
Chondrosarcoma: cartilage-based tumor, common in older adults
Giant Cell Tumor: soap-bubble appearance on X-ray