Giant cell tumour of bone most commonly affects which anatomical site and histological cell type defines its classification as a distinct entity?

• A Diaphysis of long bones; multinucleated osteoclast-like giant cells
• B Flat bones of the pelvis; aneurysmal change with blood-filled spaces
• C Epiphysis (and extending into metaphysis) of long bones in skeletally mature individuals; RANKL-expressing mononuclear stromal cells with reactive osteoclast-like giant cells ✓
• D Vertebral body; Langhans giant cells in a granulomatous background

Explanation

Giant cell tumour (GCT) of bone arises in the epiphysis of skeletally mature long bones, most commonly around the knee (distal femur, proximal tibia) and distal radius. The defining neoplastic cell is the RANKL-expressing mononuclear stromal cell (H3.3G34W mutation pathognomonic), which recruits osteoclast-like multinucleated giant cells. The giant cells are reactive, not neoplastic. This distinction is therapeutically important — denosumab (anti-RANKL antibody) targets the neoplastic stromal cells to reduce giant cell recruitment and tumour resorption.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.