A 10-year-old girl presented with leukocytosis (199×109/L), anemia (9 g/dL), and thrombocytopenia (34×109/L). After bone marrow (BM) study, she was diagnosed with B-lymphoblastic leukemia with t(4;11)(q21;q23) and
BM re-evaluation after one treatment cycle showed that 40% of total nucleated cells (TNC) comprised medium blasts with irregular-shaped nucleus, scant basophilic cytoplasm, and similar immunophenotypic characteristics as the B-lymphoblasts during initial diagnosis; however, 56% of TNCs comprised large blasts with abundant cytoplasm and round nucleus. Flow cytometry showed these were similar to monoblasts and positive for CD64, CD4, CD15, and CD33 (
Acute leukemia lineage switch is rare and has poor outcome.