A 57-year-old woman with no known medical history presented with fatigue and weakness. Her complete blood count showed white blood cell count, 413.6 × 10⁹/L; hemoglobin level, 83 g/L; and platelet count, 244 × 10⁹/L. A review of the peripheral blood smear showed 37% blasts with irregular nuclear contours, fine chromatin, and scant agranular cytoplasm. Other prominent findings included leukocytosis with left shift, mild basophilia, and eosinophilia (panels A-F; original magnification, ×1000). Flow cytometry of a peripheral blood specimen showed 34% blasts with the following immunophenotype: CD19⁺/CD10⁺/cytoCD22⁺/cytoCD79a⁺/TdT⁺/CD34partial⁺/CD20partial⁺/CD38(decreased⁺)/CD45 dim⁺/cytoCD3⁻/MPO⁻/κ⁻/λ⁻ (panel G), diagnostic of B-cell acute lymphoblastic leukemia (B-ALL). Left-shifted myeloid maturation and eosinophilia were illustrated by flow cytometric immunophenotyping (panel G). Concurrent cytogenetics analysis showed an abnormal karyotype: 46,XX,t(9;22)(q34.1;q11.2)[17]/47,idem,+der(22)t(9;22)(q34.1;q11.2)[3]. Fluorescence in situ hybridization with a tricolor, dual-fusion BCR/ABL1 probe set revealed 77.5% cells with dual-fusion signals (1R1G2F2A) and 16.5% with an abnormal pattern (1G3F1A). Molecular testing by reverse transcription polymerase chain reaction showed a p210 BCR-ABL1 fusion transcript. Subsequent bone marrow biopsy showed 90% to 100% cellularity predominantly involved by B-ALL.

The overall findings in this case were diagnostic of B-ALL. The clinical and laboratory features were highly suggestive of the B-lymphoid blast phase of chronic myeloid leukemia (CML). This case is an example of leukocytosis with myeloid left-shift maturation providing a clue for diagnosing the B-lymphoid blast phase in a patient with undiagnosed CML.

Figure edited by Amaris Shi, Clements High School, Sugar Land, TX.