Isolated add(12)(p13) in a BCR::ABL1-Negative Neutrophilic Myeloproliferative Neoplasm Lacking Canonical Driver Mutations: A Case Report

Persistent neutrophilic leukocytosis with hepatosplenomegaly raises suspicion for chronic neutrophilic leukemia (CNL) and other BCR::ABL1-negative myeloid neoplasms, but diagnosis can be challenging when canonical driver mutations such as colony-stimulating factor 3 receptor (CSF3R) are absent.We report a 53year-old man with persistent leukocytosis (total leukocyte count 64.7 × 10⁹/L) with marked neutrophilia, left-shifted granulopoiesis, and hepatosplenomegaly.BCR::ABL1 polymerase chain reaction (PCR) was negative.Bone marrow examination showed a hypercellular marrow with granulocytic predominance and a normal leukocyte alkaline phosphatase score.Comprehensive next-generation sequencing (NGS) identified no pathogenic variants in CSF3R, Janus kinase 2 (JAK2), calreticulin (CALR), myeloproliferative leukemia protein (MPL), SET binding protein 1 (SETBP1), additional sex combs-like 1 (ASXL1), KIT proto-oncogene (KIT), FMS-like tyrosine kinase 3 (FLT3), nucleophosmin 1 (NPM1), or tumor protein p53 (TP53).Conventional cytogenetics revealed a 46,XY,add(12)(p13) karyotype; fluorescence in situ hybridization (FISH) for ETS variant transcription factor 6 (ETV6) rearrangement was negative.The findings were considered consistent with a BCR::ABL1-negative neutrophilic myeloid neoplasm with an indeterminate classification in the absence of a defining molecular abnormality.The isolated ETV6-negative add(12)(p13) abnormality represents an unusual cytogenetic finding, although its pathogenic significance remains uncertain because the additional genetic material was not identified.The case underscores the value of integrating clinical, morphologic, cytogenetic, and molecular findings in diagnostically challenging neutrophilic myeloid neoplasms.