Fusion genes in angiomatoid fibrous histiocytoma.

Angiomatoid fibrous histiocytoma (AFH) is a rare soft tissue tumor of low malignant potential and uncertain differentiation. Only three genetically investigated cases of AFH have been reported. Two of them displayed a FUS-ATF1 fusion gene and one showed an EWSR1-ATF1 chimera. Using RT-PCR analysis, we have identified the EWSR1-ATF1 fusion transcript, and delineated the genomic breakpoints, in two new cases of AFH. Previously, the EWSR1-ATF1 fusion protein has been suggested to activate expression of the MITF-M transcript, and therefore the expression pattern of the MITF gene was studied. The MITF-M transcript was not detected in either AFH, in line with the finding that the co-activator SOX10 was not expressed. Thus, of the five AFH that have been molecularly analyzed to date, two have displayed a FUS-ATF1 fusion gene and three have shown an EWSR1-ATF1 chimera. There is no apparent correlation between the type of fusion gene and clinicopathologic features. Nonetheless, RT-PCR for these fusion transcripts remains a valuable diagnostic adjunct in the distinction between AFH and other soft tissue tumors or metastases that may simulate it.