Hematopoietic neoplasms with FGFR1 rearrangements are rare. Clinically, patients often present with a chronic myeloproliferative neoplasm with eosinophilia and an increased risk of transformation to acute leukemia. We report a patient who initially presented with B-cell acute lymphoblastic leukemia (B-ALL) with t(8;22)(p11.2;q11.2) and an additional derivative chromosome 22 [der(22)t(8;22)]. After induction chemotherapy, B-ALL blasts were eradicated; however, a chronic myeloproliferative process emerged showing persistent t(8;22) (p11.2;q11.2) but not der(22)t(8;22). Combined morphologic and fluorescence in situ hybridization revealed that both lymphoblasts and myeloid cells harbored t(8;22)(p11.2;q11.2); but only lymphoblasts carried the additional der(22)t(8;22). This case provides direct evidence to illustrate the clonal relationship of chronic phase and blast phase in myeloid neoplasms with FGFR1 rearrangement, and demonstrates that clonal cytogenetic evolution plays an important role in disease progression.