Basophilic differentiation of leukemic cells in a patient with acute leukemia carrying minor bcr/abl chimeric mRNA

A 77-year-old woman was referred to our hospital because of leukocytosis and leukoblastosis in September 1999. She was healthy except for hypertension, and no abnormal findings in the peripheral blood had been observed up to December 1998. Physical examination revealed neither hepatosplenomegaly nor superficial lymphadenopathy. A bone marrow film showed massive proliferation of blast cells (87.8%), some of which contained coarse basophilic granules (38.6%). The cells were negative for peroxidase and esterase (alpha-naphtyl butyrate and ASD-chloroacetate) staining, but the granules showed metachromasia upon toluidine blue staining. As immunophenotypic analysis of the cells showed double positive for CD13/CD19 but negativity for CD33, this case did not meet the diagnostic criteria for biphenotypic acute leukemia. Chromosome and gene analysis showed positivity for the Ph1 chromosome with minor bcr/abl chimeric mRNA. A homogenate of the peripheral mononuclear cells demonstrated a high concentration of histamine. Electron microscopy analysis confirmed that some of the blast cells contained dense granules, which closely resembled "immature basophil granules" morphologically. These results suggested that the blast cells showed basophilic differentiation. As the clinical course and peripheral blood findings were different from blastic crisis of chronic myelogenous leukemia (CML) and CML with minor bcr/abl chimeric mRNA, the present case was diagnosed as "multiphenotypic acute leukemia", a type of acute basophilic leukemia classified by Duchayne.