FGFR1 and atypical chronic myeloid leukemia, BCR-ABL1 negative: The fusion of BCR and fibroblast growth factor receptor 1 (FGFR1) arises from the t(8;22) (p11;q11) translocation, occurring commonly in EMS or stem cell leukemia (SCLL) but also observed in AML, atypical chronic myeloid leukemia (aCML) and B-cell lymphomas.