Characterization of MLL/AF4 lineage-switched cases. (A) Morphological change from lymphoblastic leukemia (left) to acute monoblastic/monocytic leukemia (right) in patient LS01. Bar represents 20 μm. (B) Sanger sequencing of MLL/AF4 and reciprocal AF4/MLL fusions in LS01 presentation ALL (top) and relapsed AML (bottom) identifies a common breakpoint with identical filler sequences in the ALL and AML samples.