Consistency of Radiological Staging in Resectable Mismatch-Repair Proficient Colon Cancer: An Interobserver Agreement Study

Background Reproducibility and accuracy of radiological staging with CT imaging is crucial for selecting patients with resectable, non-metastatic colon cancer (CC) who may benefit from neoadjuvant strategies. Methods We evaluated interobserver agreement among four independent radiology equipes in staging patients with resectable, non-metastatic, mismatch repair proficient CC with available preoperative CT imaging. Radiology equipes were blinded to clinical and pathological data, and categorized tumors according to FOxTROT/OPTICAL and Node-RADS criteria, classifying T (T1/2, T3, T4, including stratification by extramural invasion [EMI]) and N status. The primary endpoint was interobserver agreement (Cohen's κw); secondary endpoints included concordance with pathological staging and diagnostic performance metrics. Bayesian and cross-validation analyses assessed robustness. Results Among 109 patients (32% pT2, 34% pT3, 34% pT4; 46% pN0/1c, 54% pN1–2), overall interobserver agreement indicated inadequate concordance for both cT (κw = 0.56; 95% CI, 0.43–0.68) and cN category (κw = 0.51; 95% CI, 0.36–0.66). Of 109 patients, 38 (35%) were staged identically for T stage by all four Radiology groups, while 71 (65%) showed some disagreement. When considering risk stratification into high risk (cT3 with EMI ≥5 or cT4) versus low risk (cT1/cT2 or cT3 with EMI