A 20-year-old man presents with a lytic lesion in the epiphysis of the distal femur extending to the subchondral plate. Biopsy shows numerous osteoclast-type multinucleated giant cells uniformly distributed among round to oval mononuclear stromal cells. What is the neoplastic cell in this tumor?
- A Mononuclear stromal cells ✓
- B Osteoclast-type multinucleated giant cells
- C Osteoblasts
- D Chondroblasts
Correct answer: A. Mononuclear stromal cells
Explanation
In giant cell tumor of bone, the neoplastic cells are the mononuclear stromal cells that express RANKL and drive recruitment of reactive osteoclast-type giant cells. The giant cells themselves are reactive and non-neoplastic. This distinction is fundamental to understanding GCT biology and the rationale for denosumab (RANKL inhibitor) therapy.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.