Introduction: Acute myeloid leukemia (AML) with inv(16)(p13.1q22) or t(16;16)(p13.1;q22) is a genetically defined core-binding-factor AML, usually associated with the CBFB::MYH11 fusion. Although the classic marrow pattern combines myelomonocytic differentiation with abnormal eosinophils, the abnormal eosinophilic component may be focal or numerically subordinate to the blast and monocytic populations.Case report: A 25-year-old man presented with severe anemia, thrombocytopenia, leukocytosis, fever, fatigue, cough, pallor, and mild hepatosplenomegaly. A 500-cell bone marrow differential count showed 44% conventional blasts, 20% monoblasts/promonocytes, 6% monocytes, 12% eosinophils, 8% abnormal eosinophil precursors, and 10% lymphocytes. Because monoblasts and promonocytes are blast equivalents, the blast-equivalent burden was 64%. Abnormal eosinophilic precursors contained coarse basophilic granules, and a harlequin-type eosinophils was identified. An outside flow cytometry report described a primitive CD34/CD117/CD13/CD33-positive blast population with aberrant CD7 and a second monoblastic/monocytic population. Conventional cytogenetics showed 46,XY,inv(16)(p13.1q22)[15]/46,XY[5]. CBFB break-apart fluorescence in situ hybridization (FISH) demonstrated a 1F1R1G split-signal pattern in 160 of 200 nuclei, above the laboratory cutoff of 3%.Conclusion: AML with inv(16) may show a non-dominant but diagnostically important abnormal eosinophilic component. In this case, coarse basophilic granules and a harlequin-type eosinophils provided the key morphologic clue, while karyotyping and CBFB break-apart FISH confirmed the diagnosis. Careful integration of morphology, flow cytometry, cytogenetics, and molecular testing when available is essential for accurate classification and appropriate measurable residual disease monitoring

Background: Interstitial duplications of the long arm of chromosome 11 are rare constitutional chromosomal abnormalities with considerable phenotypic variability. Clinical manifestations depend on the location and extent of the duplicated segment and may include prenatal and postnatal growth impairment, developmental delay, hypotonia, craniofacial dysmorphism, limb abnormalities, and congenital heart defects. Because many clinically significant chromosomal duplications are sufficiently large to produce a visible alteration in chromosome morphology, conventional karyotyping remains useful for their initial detection and structural characterization.Case presentation: A 6-month-old boy was evaluated for prenatal and postnatal growth restriction, feeding difficulty, generalized hypotonia, predominantly motor developmental delay, microcephaly, craniofacial dysmorphism, minor limb abnormalities, and a small muscular ventricular septal defect. Conventional cytogenetic analysis of peripheral-blood lymphocytes using GTG banding at approximately 450–550-band resolution demonstrated additional chromosomal material within the long arm of one chromosome 11. Analysis of at least 30 metaphases consistently showed the abnormality, establishing the karyotype as 46,XY,dup(11)(q21q23) and confirming an interstitial duplication of 11q21–q23 with partial trisomy of the duplicated segment. No additional numerical or structural chromosome abnormality was detected at the resolution of the study. Chromosomal microarray and fluorescence in situ hybridization were not performed; therefore, the precise genomic coordinates, size, orientation, and gene content of the duplicated segment could not be determined. Parental karyotyping was recommended to clarify whether the rearrangement was de novo or inherited.Conclusion: This case demonstrates that conventional GTG-banded karyotyping can provide a definitive cytogenetic diagnosis when a constitutional duplication is large enough to be resolved at chromosome-band level. In addition to identifying the involved chromosome and duplicated region, karyotyping provides a genome-wide assessment for accompanying numerical or structural abnormalities and forms an important basis for parental studies and recurrence-risk counseling.