Neutrophil Extracellular Trap is Surrogate Biomarker for Prognosis and Response to Neoadjuvant Therapy in Locally Advanced Rectal Cancer

Purpose: To demonstrate the intrinsic association of Neutrophil extracellular traps (NETs) with outcome and neoadjuvant therapy response of locally advanced rectal cancer (LARC), and the mechanisms.Patients and Methods: We enrolled 240 patients with LARC who underwent surgery without neoadjuvant therapy in two independent sets (training and validation), and 153 patients who received neoadjuvant therapy with biopsy followed by surgery. Immunohistochemistry, immunofluorescence staining and bioinformatics analysis were performed in formalin-fixed paraffinembedded sections. NETs were identified by costaining for myeloperoxidase and citrullinated histone H3.Results: NETs were associated with recurrence-free survival in the surgical training and validation sets. High-NET density predicted poor postoperative survival of patients with LARC. Multivariate analysis identified NETs, TNM stage, and neutrophil-to-lymphocyte ratio as independent prognostic factors for recurrence-free survival. Low-NETs LARC demonstrated increased CD8+ T cell and lower T regulatory cell infiltration, which indicated a tumor immune microenvironment with strong antitumor capacity. High-NET density was associated with epithelial-mesenchymal transition, which is considered to contribute to tumor progression. In the neoadjuvant therapy cohort, high-NET density on biopsy was significantly associated with reduced likelihood of complete/near complete response.Conclusion: NET was an independent prognostic factor in LARC that were associated with patients' survival, and NET density in pretreatment biopsies was an independent predictive biomarker of response to neoadjuvant therapy. This biomarker may be helpful in predicting survival in LARC with improved accuracy and selecting patients who will respond to neoadjuvant therapy.