Fusion of the HMGA2 and NFIB genes in lipoma

The major cytogenetic subgroup of lipomas is characterized by aberrations of chromosome segment 12q13-15, which recombines with a large number of other chromosomal regions. The gene HMGA2 is the main target in these aberrations. For some recurrent rearrangements, chimeric transcripts, including the 5' part of HMGA2, have been described. The 3' partners identified are LPP, LHFP, CMKOR1, and EBF. In addition, subsets of other benign solid tumors show aberrations of 12q13-15. Among pleomorphic adenomas of the salivary glands, where the preferred recombination partner with 12q13-15 is 9p22-24, an HMGA2/NFIB fusion gene has been reported. In the present study, two cases of lipoma with rearrangements of 9p22-24 and 12q15 were analyzed by reverse transcription polymerase chain reaction to find out if HMGA2/NFIB was also present in lipoma. An in-frame fusion transcript, combining the four first exons of HMGA2 with exon 8 of NFIB, was detected in one case. It was identical to a transcript that was previously described in salivary gland adenoma and contained a stop codon shortly 3' of the fusion point. The finding of the same fusion gene in different tumors is not unique. For example, HMGA2/LPP has been reported in lipoma, pulmonary chondroid hamartoma, and soft tissue chondroma. Since similar 9;12 translocations have been described also in rare cases of hamartoma and uterine leiomyoma, the occurrence of HMGA2/NFIB could be postulated in these tumors as well.