Bone marrow aspiration (A, Wright stain, ×1,000), myeloperoxidase cytochemical stain (B, ×1,000), biopsy (C, H&E stain, ×1,000), and karyotype results (D) performed for our patient at the time of relapse. The patient's bone marrow aspiration shows infiltration of leukemic blasts using myeloperoxidase cytochemical stain positivity (A and B). The biopsy section also shows normocellularity with infiltration of leukemic blasts (C). His karyotype result obtained at relapse showed 46,XY, t(6;7)(p21.3;p22)[4]/46,XY[26] (the two breakpoint lesions are indicated with a black arrow), indicating the emergence of a solitary t(6;7)(p21.3;p22) passenger translocation with a frequency of 13.3% at relapse (D).