Genetic Mutational Profile Influences the Morphological Characteristics of Abnormal Monocytes in Patients with Juvenile Myelomonocytic Leukemia

INTRODUCTION: Juvenile myelomonocytic leukemia (JMML) is characterized by excessive myelomonocytic cell proliferation and hypersensitivity to granulocyte-macrophage colony-stimulating factor. Five canonical RAS pathway gene mutations (PTPN11, NF1, KRAS, NRAS, and CBL) are known to be involved in the pathogenesis of JMML. Patients with JMML typically exhibit erythroblasts and myeloid progenitor cells, as well as an increase in abnormal monocytes (≥1.0 × 10⁹/L), in their peripheral blood. However, the characteristic morphological abnormalities of increased monocytes have not been systematically evaluated in a large cohort of patients. This study aimed to evaluate the morphological characteristics of abnormal monocytes and their association with genetic profiles in patients with JMML.

METHODS: This study included 92 Japanese patients who were genetically evaluated and diagnosed with JMML (n = 77) or Noonan syndrome-associated myeloproliferative disorder (n = 15) based on internationally accepted criteria. The median age at diagnosis was 10 months (range: 0–112 months). Morphological characteristics were evaluated in 9,200 abnormal monocytes in peripheral blood across the entire cohort, with 100 monocytes examined in each case. Peripheral blood smears were evaluated by physicians (DY and AH) with expertise in pediatric hematological morphology. The study was approved by the ethics committee of Nagoya University Graduate School of Medicine and conducted in accordance with the principles of the Declaration of Helsinki.

RESULTS: Based on somatic/germline mutations in the canonical five RAS pathway genes, patients were classified into six groups: PTPN11_somatic (n = 27), NF1_JMML (n = 5), KRAS_JMML (n = 16), NRAS_JMML (n = 14), CBL_JMML (n = 15), and PTPN11_germline (n = 15). A total of 9,200 abnormal monocytes from 92 patients were morphologically classified into four types based on their nuclear shape (club-shaped vs. round-shaped) and the presence or absence of cytoplasmic vacuoles: type A (23.6%, club-shaped nuclei with cytoplasmic vacuoles), type B (19.4%, club-shaped nuclei without cytoplasmic vacuoles), type C (30.7%, round-shaped nuclei with cytoplasmic vacuoles), and type D (26.3%, round-shaped nuclei without cytoplasmic vacuoles). The PTPN11_somatic group had significantly more type A monocytes (median 34.0%, p = 2.29 × 10⁻³), the PTPN11_germline group had more type B monocytes (median 26.0%, p = 6.67 × 10⁻³), the KRAS_JMML group had more type C monocytes (median 41.0%, p = 3.65 × 10⁻²), and the NRAS_JMML group had more type D monocytes (median 48.5%, p = 1.03 × 10⁻⁵). Patients with higher type A monocytes (≥ 20.5%) showed a significantly worse overall survival rate compared to those with lower type A monocytes (5-year OS: 34.6% [95% confidence interval (CI); 17.5%–52.5%] vs. 64.0% [95% CI; 38.5%–76.1%], p = 0.0183).

DISCUSSION: Our findings indicate that the genetic mutational profile influences the morphological characteristics of abnormal monocytes in patients with JMML. We are currently developing an artificial intelligence model capable of automatically classifying abnormal monocytes in JMML to predict the genetic profile and prognosis of patients with JMML. This analysis is expected to result in the development of quantitative and reproducible morphological indicators, achievable through methods such as machine learning.