Accuracy of Computed Tomography Staging of Mismatch Repair-Deficient Colon Cancer

PURPOSE This study assesses the accuracy of radiographic clinical staging by computed tomography (CT) of mismatch repair-deficient (dMMR) colon cancer, given emerging data for neoadjuvant immune checkpoint inhibitors (ICIs). METHODS Patients with stage I-III colon cancer treated with upfront surgical resection were retrospectively reviewed using the electronic medical record from a single institution from 2012 to 2023. We performed a cohort study of dMMR tumors with a stage-matched control cohort of mismatch repair-proficient (pMMR) tumors. The primary end point was the accuracy of clinical stage using preoperative CT compared with pathologic stage for dMMR colon cancer. Statistical analysis was performed using R. RESULTS We identified 78 patients with dMMR colon cancer. For dMMR tumors, T-stage clinical radiologic staging matched pathologic stage in 51% of cases and the nodal stage was accurately matched in 55% of cases. For stage I and IIA (low-risk) tumors, the overstaging rate on CT was 41% and for T4 or N+ (high-risk), the understaging rate was 25%. When comparing the dMMR and pMMR cohorts, pMMR nodal status was more likely to be understaged ( P < .001). There was moderate to substantial interrater reliability for overall stage, T stage, and N staging between radiologists (kappa = 0.64, 0.60, and 0.63, respectively). CONCLUSION Radiographic tumor and nodal staging for dMMR colon tumors is unreliable with high rates of overstaging low-risk tumors where neoadjuvant treatment may not be indicated. The low accuracy of clinical staging demonstrates clear limitations to make systemic therapy decisions. Additional diagnostic modalities for lymph node status may be necessary to accurately clinically stage patients before neoadjuvant ICIs in patients with locally advanced disease.