Characteristics of MLL-EP300-positive therapy-related myeloid neoplasm in the present case. (a) Bone marrow (BM) showed numerous differentiated monocytes without any increase in the number of myeloblasts or adult T-cell lymphoma/leukemia (ATL) cells (May–Giemsa stain, original magnification, 1,000x). Some monocytes exhibited slightly atypical nuclei. (b) Fluorescence in situ hybridization (FISH) analysis for gene rearrangements involving in the mixed lineage leukemia (MLL) gene at 11q23 was performed. The normal MLL gene exhibited a yellow signal (arrow head), whereas a split MLL gene exhibited as a pair of green and red signals (arrows). The BM sample from the present case showed that 78.5% of the interphase cells were positive for the split MLL gene signals. (c) G-banding of the BM material revealed 46,XX, t(11;22)(q23;q13)/46,XX. Red arrows indicate the abnormal chromosomes involving the translocation. (d) Human T-cell leukemia virus type 1 (HTLV-1) provirus DNA analysis was performed by using inverse polymerase chain reaction. CD14-sorted monocytes (lanes 1, 2) showed no bands. CD3-sorted T-cells (lanes 3, 4) failed to show a visible band with the reproducibility, indicating that the case was negative for a major ATL clone. TL-Om1 was an HTLV-1-infected cell line as positive control (lane 5), and distilled and deionized water (DDW) was used for negative control (lane 6).