Background/Objectives: Systemic inflammatory responses influence treatment response and oncological outcomes in patients with cancer. Growing evidence indicates that the inflammatory burden index (IBI) serves as a reliable prognostic indicator across various malignancies. However, the clinical significance of the peri-treatment inflammatory status in patients with rectal cancer (RC) undergoing preoperative chemoradiotherapy (CRT) remains unclear. Methods: We assessed the pre- and post-treatment IBI in 97 patients with RC who received preoperative CRT followed by total mesorectal excision at our institution. Results: Although no significant changes were observed in the pre- or post-CRT IBI and no associations were found with most clinicopathological factors, survival analysis revealed that a high pre-CRT IBI was significantly associated with shorter overall survival (OS) and disease-free survival (DFS). Multivariable analysis revealed that a high pre-CRT IBI and pathological lymph node metastasis remained independent prognostic factors for both outcomes. Subgroup analysis demonstrated that the prognostic value of the peri-treatment IBI differed according to the ypN status, with the pre-CRT IBI showing particularly strong prognostic performance in patients without pathological lymph node metastasis (ypN−). Conclusions: Pre-treatment assessment of the IBI may improve risk stratification in patients with RC undergoing preoperative CRT followed by curative resection.

Background/Objectives. Systemic inflammatory responses influence treatment response and oncological outcomes in patients with cancer. Growing evidence indicates that the inflammatory burden index (IBI) serves as a reliable prognostic indicator across various malignancies. However, the clinical significance of the peri-treatment inflammatory status in patients with RC undergoing preoperative chemoradiotherapy (CRT) remains unclear. Methods. We assessed the pre- and post-treatment IBI in 97 patients with rectal cancer (RC) who received preoperative CRT followed by total mesorectal excision at our institution. Results. Although no significant changes were observed in the pre- or post-CRT IBI and no associations were found with most clinicopathological factors, survival analysis revealed that a high pre-CRT IBI was significantly associated with shorter overall survival (OS) and disease-free survival (DFS). Multivariable analysis revealed that a high pre-CRT IBI and pathological lymph node metastasis remained independent prognostic factors for both outcomes. Subgroup analysis demonstrated that the prognostic value of the peri-treatment IBI differed according to the ypN status, with the pre-CRT IBI showing particularly strong prognostic performance in patients without pathological lymph node metastasis (ypN−). Conclusion. Pre-treatment assessment of the IBI may improve risk stratification in patients with RC undergoing preoperative CRT followed by curative resection.