The RREB1-TFE3 gene fusion found in the intermediate grade myofibroblastic sarcoma SARC3 fuses the first eight exons of RREB1 to the last nine exons of TFE3, preserving the open reading frame of both RREB1 and TFE3. The fusion is predicted to interrupt expression of RREB1 (Table 2), indicating that RREB1-TFE3 is the dominantly expressed RREB1 allele. The gene discussed is RREB1; the disease is sarcoma.