A 74-year-old with colorectal carcinoma treated with surgery and adjuvant chemotherapy 6 years previously was admitted with fever and sepsis. Laboratory tests showed hemoglobin 137 g/L, mean corpuscular volume 94.7 fL, platelets 177 × 109/L, leukocytes 2.0 × 109/L, and neutrophils 0.8 × 109/L. He deteriorated with progressive pancytopenia a. A blood smear showed hyposegmented neutrophils (pseudo–Peger-Huët cells) and abnormal granulation ( panel A). A bone marrow aspirate revealed markedly dysplastic changes affecting granulocytic precursors with multinucleated forms and dysplastic granulation (panel B, panel C ). Cytogenetic analysis showed a complex karyotype with multiple numeric and structural anomalies (panel D; G-banded karyogram of 1 metaphase cell of the bone marrow showing hypotetraploidy with 88 chromosomes and multiple anomalies including several derivative and dicentric chromosomes, duplications, robertson translocations, and 5 markers).