Circulating Cit-H3 and MPO-DNA complexes reveal divergent neutrophil-associated immune profiles in multiple myeloma

Neutrophils are increasingly recognized as dynamic regulators of tumor inflammation and immune remodeling. Neutrophil extracellular trap (NET)-related biomarkers have been implicated in cancer progression, but their clinical and immunological interpretation remains challenging because different circulating NET components may not represent equivalent biological processes. In multiple myeloma, a malignancy shaped by complex interactions among clonal plasma cells, hematopoiesis, and the bone marrow immune microenvironment, the relevance of distinct circulating NET-related markers remains unclear.

We measured serum citrullinated histone H3 (Cit-H3) and myeloperoxidase-DNA complexes (MPO-DNA) in 171 patients with multiple myeloma and 15 healthy controls. Patients were categorized by disease status at sampling as newly diagnosed multiple myeloma, remission, or relapsed/refractory multiple myeloma. Associations with disease status, inflammatory parameters, tumor burden, hematologic indices, R-ISS and R2-ISS stage, high-risk cytogenetic abnormalities, and exploratory survival outcomes were analyzed.

Serum Cit-H3 levels were significantly higher in patients with multiple myeloma than in healthy controls and were highest in relapsed/refractory disease. Cit-H3 was associated with lower lymphocyte counts and higher neutrophil-to-lymphocyte ratios. In contrast, serum MPO-DNA complexes were not significantly increased in the overall myeloma cohort compared with controls and were lower in relapsed/refractory disease than in newly diagnosed or remission states. In exploratory correlation analyses, higher MPO-DNA levels were associated with higher hemoglobin and albumin levels, lower bone marrow plasma cell burden, and lower β2-microglobulin. Cit-H3 and MPO-DNA levels were not significantly correlated, and neither marker was significantly associated with R-ISS or R2-ISS stage, del(17p), t(4;14), or 1q21 amplification. Exploratory survival analyses showed no statistically significant associations with progression-free or overall survival.

Circulating Cit-H3 and MPO-DNA complexes are not interchangeable NET-related biomarkers in multiple myeloma and do not simply reflect conventional clinical or cytogenetic risk stratification. Rather than representing a uniform NET signal, these markers may capture distinct aspects of neutrophil-related immune dysregulation, systemic inflammation, and hematopoietic status, highlighting the need for prospective validation.