Malignant fibrous histiocytoma of bone: analysis of genomic imbalances by comparative genomic hybridisation and C-MYC expression by immunohistochemistry.

Malignant fibrous histiocytoma (MFH) of bone is a rare, highly malignant tumour. As very little is known about its genetic alterations, 26 bone MFHs were analysed by comparative genomic hybridisation (CGH). Twenty-three tumours (89%) had DNA sequence copy number changes (mean, 7.2 changes per sample). Gains were more frequent than losses (gains:losses=2.5:1). Minimal common regions for the most frequent gains were 8q21.3-qter (35%), 9q32-qter (35%), 7q22-q31 (35%), 1q21-q23 (31%), 7p12-pter (31%), 7cen-q11.2 (31%) and 15q21 (31%). Minimal common regions for the most frequent losses were 13q21-q22 (42%) and 18q12-q22 (27%). High-level amplifications were detected in 8 out of the 26 tumours (31%). The only recurrent amplifications, 1q21-q23 and 8q21.2-q22, were present in two samples (8%). As copy number increase at 8q24 (the locus of C-MYC) was frequent, the expression of C-MYC was studied by immunohistochemistry. Increased levels of c-myc protein were detected in 7 out of 21 tumours studied (33%). 81% of the samples studied both by CGH and immunohistochemistry showed concordant results. Furthermore, the findings of the present study were compared to previous publications on osteosarcoma, soft tissue MFH and fibrosarcoma of bone. Clear differences were detected in CGH aberration patterns, further supporting the concept of bone MFH as an individual bone tumour entity. Finally, the findings of the present study reflect well the high malignancy and aggressive nature of bone MFH.