Association of Pre-treatment CALLY Index With Pathological Response to Neoadjuvant Chemotherapy in Rectal Cancer

<h3>Background/Aim:</h3> Neoadjuvant chemotherapy (NAC) without radiotherapy is performed in selected patients with locally advanced rectal cancer (LARC); however, reliable predictors of pathological response remain unclear. This study aimed to explore the association between systemic inflammatory markers, particularly the C-reactive protein (CRP)-albumin-lymphocyte (CALLY) index, and pathological response to NAC. <h3>Patients and Methods:</h3> Fifty-nine patients with clinical stage II-III rectal cancer treated with NAC followed by surgery between 2018 and 2026 were retrospectively analyzed. Pathological response was evaluated according to the Japanese Classification of Colorectal, Appendiceal, and Anal Carcinoma (ninth edition) and categorized into non-responders (grade 0-1) and responders (Grade 2-3). Pre-treatment CRP, CRP-to-albumin ratio (CAR), and CALLY index were assessed. Univariate logistic regression and receiver operating characteristic (ROC) analyses were performed. <h3>Results:</h3> Twenty-four patients (40.7%) achieved grade 2-3 response. The number of NAC cycles was significantly higher for responders than for non-responders (<i>p</i>=0.021). Targeted therapy was more frequently used in responders than in non-responders (87.5% <i>vs.</i> 54.3%, <i>p</i>=0.010). In univariate logistic regression analysis, log(CRP) showed a borderline association with response [odds ratio (OR)=0.43, 95% confidence interval (CI)=0.19-1.00, <i>p</i>=0.051]. Log(CAR) (OR=0.46, 95% CI=0.21-1.04, <i>p</i>=0.061) and log(CALLY index) (OR=2.19, 95% CI=0.97-4.95, <i>p</i>=0.061) showed similar borderline associations. Receiver operating characteristics analysis demonstrated comparable discriminatory ability among markers (with area under the curves ranged from 0.656 to 0.663). <h3>Conclusion:</h3> Pre-treatment inflammatory markers, including the CALLY index, may help predict pathological response to NAC in locally advanced rectal cancer.