A 17-year-old boy is brought to the physician because of progressive right knee pain for the past 3 months. He reports that the pain is worse at night and while doing sports at school. He has not had any trauma to the knee or any previous problems with his joints. His vital signs are within normal limits. Examination of the right knee shows mild swelling and tenderness without warmth or erythema; the range of motion is limited. X-rays reveal a large lytic lesion involving the proximal tibia with extensive soft-tissue swelling. Histologic examination of the mass is shown in the exhibits.
Which of the following is the most likely diagnosis?

Question

A 17-year-old boy is brought to the physician because of progressive right knee pain for the past 3 months. He reports that the pain is worse at night and while doing sports at school. He has not had any trauma to the knee or any previous problems with his joints. His vital signs are within normal limits. Examination of the right knee shows mild swelling and tenderness without warmth or erythema; the range of motion is limited. X-rays reveal a large lytic lesion involving the proximal tibia with extensive soft-tissue swelling.  Histologic examination of the mass is shown in the exhibits.   
Which of the following is the most likely diagnosis?

Quizplus · Accepted Answer

Eductional Objective: Osteosarcoma is the most common primary bone tumor in children and young adults and typically arises near the metaphyses of long bones.  Patients usually have slowly worsening pain and soft-tissue swelling.  X-ray typically reveals a lytic bone lesion, and biopsy classically shows pleomorphic, spindle-shaped tumor cells that generate osteoid and thin trabeculae of neoplastic bone.

A 17-Year-Old Boy Is Brought to the Physician Because of Progressive