Beyond the Ordinary: An Unusual Case of Chronic Myelomonocytic Leukemia with Homogeneously Staining Regions in 11q

Abstract Chronic myelomonocytic leukemia (CMML) is a rare clonal hematological malignancy primarily affecting older adults, presenting with symptoms of myelodysplastic Syndrome (MDSs) and myeloproliferative neoplasms. It is characterized by persistent monocytosis, bone marrow dysplasia, and genetic abnormalities. Here, we describe a unique case of CMML in a 66-year-old male with complex karyotype containing a homogeneously staining region (hsr) of chromosome 11q. The patient had clinical symptoms of fever, cough, and dyspnea along with underlying conditions of anemia, thrombocytopenia, and leukocytosis. Monocytosis (49%) and 4% blasts were observed in blood smear and bone marrow studies. Karyotyping revealed several chromosomal aberrations, including derivative chromosome (3;12), 5q deletion, 21 chromosome loss, and hsr on the chromosome 11 long arm. The presence of hsr is rare in hematological malignancies. Fluorescence in situ hybridization analysis revealed a KMT2A gene amplification in the 11q23 region, reported in 1% of myeloid malignancies including acute myeloid leukemia and MDSs. It is crucial in tumorigenesis, driving therapeutic interventions and associated with poor prognosis. This case underscores the importance of cytogenetics in routine CMML workups and the need for exploration in cases where comprehensive genetic tests are unavailable.