Uterine leiomyomas are smooth muscle tumors most commonly seen in middle-aged women. Approximately 10% of these tumors contain rearrangements of the chromatin-remodeling gene HMGA2 at the chromosome band 12q14.3. Herein, we report on a uterine leiomyoma with a novel HMGA2 fusion gene. A 44-year-old woman presented with a 20-cm mass uterine leiomyoma. From a histological standpoint, the tumor exhibited extensive hyalinization, very low mitotic activity (<1/10 HPH), and no cytologic atypia. Smooth muscle differentiation was confirmed by the expression of smooth muscle actin and desmin. Standard cytogenetic analysis showed the reciprocal translocation t(7;12)(q31.2;q14.3). Fluorescence in situ hybridization analysis confirmed a balanced rearrangement of the HMGA2 locus in 80% of the cells. 3'RACE reverse-transcription polymerase chain reaction identified the fusion of HMGA2 exon 4 to the COG5 locus on 7q31 (component of oligomeric golgi complex 5 isoform). The fusion sequence is predicted to encode a 96-amino acid chimeric protein that retains all three DNA-binding domains (AT hooks) of HMGA2, but that is shorter than the original HMGA2 protein. Since the general structure of the fusion gene is similar to other previously described HMGA2 fusions, its biologic activity is predicted to be likely similar.
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