Deficient Mismatch Repair, Mucinous Histology, and Systemic Inflammation Are Associated with Nodal Overstaging on Preoperative Computed Tomography in Right-Sided Colon Cancer: A Propensity Score–Matched Study

Abstract Background Accurate preoperative nodal staging is increasingly important as neoadjuvant immunotherapy emerges for mismatch repair-deficient (dMMR) colon cancer. CT-based N-overstaging may be more frequent in dMMR than in mismatch repair-proficient (pMMR) tumors; however, because dMMR status, mucinous histology, and systemic inflammation often coexist in right-sided colon cancer, we assessed their associations with nodal misclassification. Methods We retrospectively reviewed patients who underwent resection for right-sided colon adenocarcinoma. Patients with dMMR tumors were propensity score–matched to those with pMMR tumors based on age and sex, with exact matching on pT, pN, and mucinous histology. Clinicopathological, molecular, and inflammation-related factors were evaluated using logistic regression. Results The matched cohort comprised 80 dMMR and 78 pMMR patients. Among 106 pathologically node-negative patients, N-overstaging occurred in 29 (53.7%) dMMR and 19 (36.5%) pMMR tumors ( P  = 0.076). After multivariable adjustment, dMMR status (adjusted odds ratio [aOR], 2.49; 95% confidence interval [CI], 1.02–6.11; P  = 0.046), mucinous histology (aOR, 4.65; 95% CI, 1.02–21.24; P = 0.047), and modified Glasgow Prognostic Score (mGPS) 1–2 vs 0 (aOR, 5.42; 95% CI, 1.87–15.75; P  = 0.002) were associated with N-overstaging. Among 52 pathologically node-positive patients, N-understaging was less frequent in dMMR than pMMR tumors (11.5% vs 34.6%; P  = 0.048), and elevated mGPS was associated with lower odds of N-understaging ( P  = 0.030). Conclusions dMMR status, mucinous histology, and elevated mGPS emerged as independent indicators of CT-based N-overstaging in right-sided colon cancer. These tumor- and host-related factors may inform preoperative nodal assessment.