In acute leukemia of ambiguous origin with B/myeloid or trilineage phenotype (ca. 2 – 3% of all acute leukemias) and B-ALL or AML with aberrant antigen expression, the B lymphoid lineage marker CD19 and myeloid lineage marker CD33 are simultaneously displayed on the blast cell surface [1, 2]. Here, CD33 is linked to acute lymphoblastic leukemia.