Impact of MMR status on preoperative CT-based lymph node overstaging in right-sided colon cancer: a retrospective analysis

Neoadjuvant treatment for colon cancer has recently gained more and more attention. Given the imprecision of radiologic staging, low-risk patients may be exposed to the toxicities and inconvenience of chemotherapy when surgery alone might have been considered sufficient. Overstaged lymph nodes via computed tomography (CT) may lead to unnecessary neoadjuvant treatment. However, the clinical features and prognostic factors of preoperative CT-based lymph node overstaging in right-sided colon cancer, particularly the impact of mismatch repair (MMR) status, are still not well understood. This single-center retrospective cohort study enrolled 1687 patients with nonmetastatic right-sided colon cancer who underwent curative resection for primary colorectal lesions between 2013 and 2020 at the Sixth Affiliated Hospital of Sun Yat-sen University. Of these, 635 patients were assigned to the overstaged group, whereas 235 patients were assigned to the understaged group. We investigated the preoperative clinical features of overstaged groups using univariate logistic regression analysis and nomogram logistics analysis. The multivariate Cox regression analysis was used to explore the prognostic factors of the overstaged group. The deficient mismatch repair (dMMR) patients with right-sided colon cancer were more likely to be overstaged before surgery (odds ratio [OR], 1.551; 95% confidence interval [CI],1.210–1.989; P = 0.001). Overstaged patients had the best disease-free survival (DFS) (P = 0.007), while understaged patients had the worst overall survival (OS) (P = 0.001) and DFS (P < 0.001). Moreover, dMMR status was a protective factor for DFS in the overstaged group (HR = 0.535, 95% CI: 0.307–0.932; P = 0.027). Furthermore, carcinoembryonic antigen (CEA) level > 5 ng/mL, perineural invasion, and adjuvant chemotherapy were independent prognostic factors in the overstaged group. Consequently, the dMMR patients with right-sided colon cancer are more likely to be overestimated via preoperative CT scans. Patients with dMMR had a better prognosis in the overstaged group. The tendency towards nodal overstaging in dMMR right-sided colon cancer indicated there should be a more optimal assessment of CT-based lymph node staging combined with the MMR status.