Since this novel gene fusion partner of TFE3 at the 19q13.1 locus in the case herein presented is close to the BCL3 (19q13.3) gene located on the chromosome 19, interphase FISH analysis was performed on cultured and uncultured tumor cells using a dual-color break-apart DNA probe within the BCL3 gene on 19q13.3. The gene discussed is BCL3; the disease is neoplasm.