Phenotypic and molecular differences between giant cell tumor of soft tissue and its bone counterpart

Abstract

Aims

Giant cell tumor of soft tissue (GCT-ST) is a primary soft tissue neoplasm histologically similar to GCT of bone (GCT-B). Recently, it has been reported that >90% of GCT-B have a driver mutation in H3F3A gene. Since the relationship between GCT-ST and GCT-B is unclear, we compared a series of GCT-ST and GCT-B for the presence of H3F3A mutations and for several immunophenotypic markers.

Methods and Results

Eight cases of GCT-ST were retrieved from our institutional archives. Fifteen GCT-B served as controls. Direct sequencing for H3F3A mutations in coding regions between codons 1 and 42, including the hot spot codons (28, 35 and 37) was performed on DNA extracted from formalin-fixed paraffin-embedded tissue. Tumors were studied immunohistochemically for the expression of CD14, CD33, RANKL, RANK, P63 and for the osteoblastic markers SATB2 and RUNX2. None of the 7 cases of GCT-ST that could be analyzed presented H3F3A mutations, whereas 14 GCT-Bs (93.3%) were mutated. All 8 cases of GCT-ST were positive for RANK and RUNX2, while RANKL and SATB2 were detected only in 2 cases (25%). CD14 was detected only in mononuclear elements, while multinucleated giant cells and part of the mononuclear population expressed CD33. Few mononuclear cells of GCT-ST expressed P63. In comparison, GCT-B showed higher expression of p63 (14/15 cases with >50% of positive mononuclear cells), RANKL and SATB2, while CD14, CD33, RANK and RUNX2 were similarly expressed.

Conclusions

Although similar in the histologic appearance, our results indicate that GCT-ST is immunophenotypically and genetically distinct from GCT-B.

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