The impact of mismatch repair status to the preoperative staging of local colon cancer: Implications for clinical management.

Abstract

16 Background: Computed tomography (CT) scan is standard in preoperative local staging of colon cancer. Tumours with a deficient mismatch repair (dMMR) system are characterised by unique clinical and pathophysiologic aspects that may impact on the accuracy of the preoperative CT staging. Methods: Data from the Danish Colorectal Cancer Group national clinical database addressing a cohort of patients operated for stage I-III colon cancer in 2010-15 was analysed. The analyses of MMR status had been conducted consecutively through means of immunohistochemistry. All CT scans were blindly assessed by a certified radiologist. Results: Data from 590 patients, operated at a specialised cancer centre were available for analyses. A dMMR phenotype was detected in 135 (22.9%) of the patients. The overall correlation of the clinical and pathological T-category was significant for both groups. There was inferior correlation between cN and pN (p > 0.05) in pMMR cancers with a higher degree of over-staging assessed by CT-scan, compared to a significant correlation between cN and pN stage in pMMR cancers (p < 0.01). Of the 91 dMMR tumours judged node-positive by the preoperative CT scan, 59 (64.8%) showed no sign of metastatic involvement at the postoperative assessment. Conclusions: The accuracy of preoperative CT lymph node staging in colon cancer seems to differ depending on MMR status and may impact the clinical management including the neoadjuvant setting.