BCR and cancer: While most cancer-relevant fusion genes are found at low levels of recurrence in surveys of diverse tumor types, certain fusions represent hallmark drivers of cancer found at high levels of recurrence, such as BCR::ABL1 in chronic myelogenous leukemia (CML) (Kurzrock et al. 1988), SS18::SSX1 or SS18::SSX2 (Ren et al. 2013) in synovial sarcoma, and TMPRSS2::ERG (Wang et al. 2017) in prostate cancer.