A: Acute myelomonocytic leukemia with dyplastic eosinophils. Note several myeloid blasts admixed with abnormal eosinophils with large basophilic granules. Inset: Partial karyotype showing del(16)(q22) by G-banding (arrow). B: RT-PCR for detection of CBFβ-MYH11 fusion transcripts. Chemiluminescent detection of PCR products hybridized with CBFβ internal oligoprobe. Lanes are designated as follows: L, 100 bp size ladder; Pt, patient sample; (−), negative (non-specific RNA) control; W, water blank; (+), positive control for CBFβ-MYH11 (ME-1 cell line). Arrow demonstrates a 415-bp amplicon type A CBFβ-MYH11 product. C: Dual-color, break-apart FISH: large image of metaphase nucleus showing a fused red/green (yellow) signal on the q arm of one chromosome 16 and a green signal on the other arm, while the chromosome 16 homologue shows only the red signal on one arm, consistent with t(16;16)(p13;q22) [indicated by arrows]. Inset: Interphase nucleus showing a yellow fusion signal (normal configuration), as well as one green and one red signal (abnormal signal). See text for further details.