Expression of SATB2, RUNX2, and SOX9 and possible osteoblastic and chondroblastic differentiation in chondroblastoma

Chondroblastoma (CB) is histologically characterized by oval to polygonal-shaped mononuclear neoplastic cells, multinucleated osteoclastic giant cells, and eosinophilic matrix with occasional calcification. Genetically, the majority of CBs harbor H3F3B p.K36M mutation. Despite the historical nomenclature, it has been reported that the matrix of CB is similar to osteoid rather than true cartilage; however, it remains unclear whether neoplastic cells in CB have the potential for osteoblastic differentiation. To clarify this issue, we immunohistochemically examined the expression of osteogenic and chondrogenic markers (SATB2, RUNX2, p63, and SOX9) as well as H3K36M mutant protein in 33 cases of CB. All 33 cases of CB were positive for H3K36M, while SATB2, RUNX2, p63, and SOX9 were expressed in 30/33 (91%), 33/33 (100%), 29/33 (88%), and 31/32 (97%) CB cases, respectively. Our immunohistochemical results suggest that neoplastic cells in CB frequently express both osteogenic and chondrogenic markers and may have an intermediate feature of osteoblastic and chondroblastic nature.