A 28-year-old woman presents with knee pain. X-ray shows a purely lytic, expansile lesion in the distal femoral epiphysis extending to the subchondral bone plate with a soap bubble appearance. Biopsy shows sheets of uniform oval mononuclear cells interspersed with numerous multinucleated osteoclast-type giant cells. Which cells in this tumor are neoplastic?

• A The multinucleated giant cells
• B Reactive osteoblasts at the periphery
• C The oval mononuclear stromal cells ✓
• D Endothelial cells lining vascular spaces

Explanation

In giant cell tumor the mononuclear stromal cells are the neoplastic population; they express RANKL and recruit the reactive osteoclast-like giant cells, explaining local osteolysis. The lesion occurs in young adults at the epiphyseal end of long bones around the knee. The giant cells themselves are non-neoplastic recruits, which kills option A.

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.