The Presence of Neutrophil Extracellular Traps (NETs) in Brain Tumor Vessels Is Linked to Platelet Aggregates and Podoplanin in the Tumor Microenvironment

<b>Background</b>: Multiple mechanisms might lead to cancer-related hypercoagulability. In brain tumors, podoplanin, via its ability to activate platelets, seems to play a crucial role in developing venous thromboembolism (VTE). Different stimuli (including activated platelets) can trigger the release of prothrombotic neutrophil extracellular traps (NETs) by neutrophils. It remains to be elucidated whether podoplanin-induced platelet aggregates might also impact NET formation and subsequent hypercoagulability and thrombosis. <b>Methods</b>: Patients with glioma were enrolled in this prospective observational cohort study. The primary endpoint was VTE. Immunohistochemical staining of NETs (via citrullinated histone H3 [H3Cit]) and neutrophils (via myeloperoxidase [MPO]) was conducted in glioma specimens and correlated with intravascular platelet clusters (via CD61) and podoplanin. <b>Results</b>: In total, 154 patients were included. H3Cit+ tumor vessels were found in 45/154 cases. H3Cit were significantly associated with increased intravascular platelet clusters (CD61- vs. CD61+ vs. CD61++ vs. CD61+++: 3.7% (1/27) vs. 18.6% (11/59) vs. 39.4% (13/33) vs. 57.1% (20/35), <i>p</i> < 0.001) and podoplanin expression (PDPN- vs. PDPN+: 14.3% (7/49) vs. 36.2% (38/105), <i>p</i> = 0.007) in the tumor tissue. Furthermore, H3Cit+ tumor vessels were significantly associated with tumor-infiltrating MPO+ neutrophils (H3Cit- vs. H3Cit+, median [Q1-Q3]: 6.0 [3.3-12.3] vs. 12.5 [5.9-22.0] cells/mm², <i>p</i> < 0.001) and with D-dimer levels (H3Cit- vs. H3Cit+: 0.53 [0.32-1.10] vs. 0.84 [0.46-2.75] µg/mL, <i>p</i> = 0.034). The VTE risk was not linked to H3Cit+ tumor vessels (<i>p</i> = 0.613, log-rank). <b>Conclusions</b>: H3Cit in tumor vessels was not associated with VTE. However, H3Cit was linked to a local procoagulant phenotype in glioma, thereby potentially contributing to a systemic hypercoagulable state and thrombus formation.