SS18 and chronic myelogenous leukemia, BCR-ABL1 positive: In cancer, gene fusions typically result from chromosomal rearrangements, including well-known drivers of cancer, such as BCR::ABL1 in chronic myelogenous leukemia (CML),1,2 TMPRSS2::ERG in prostate cancer,3,4 and SS18::SSX1 or SS18::SSX2 in synovial sarcoma.5