The impact of mismatch repair status and systemic inflammatory markers on radiological staging in colon cancer

Objective: Mismatch repair (MMR) deficient (dMMR) colon cancer (CC) is distinct from MMR proficient (pMMR) CC, yet the impact of MMR status on radiolog-ical staging is unclear. The purpose of this study was to investigate how MMR status impacts CC CT staging. Methods: We retrospectively compared CT staging accuracy between dMMR and pMMR CC patients under-going curative resection. Accuracy was assessed as indi-vidual tumour (T)/nodal (N) stages and as dichotomous "statuses" (T1/2 vs T3/4; N0 vs N1/2). Patient character-istics were analysed for factors to support staging. Results: There was no significant difference in overall staging accuracy between the dMMR (44 patients) and pMMR (57 patients) groups. dMMR tumours with incor-rect N stage/"status" were more likely to be overstaged than pMMR tumours (90% vs 59%; p = 0.023 for "N status"). Platelet count, CRP and neutrophil count (AUC 0.76 (p = 0.0078), 0.75 (p = 0.034) and 0.70 (p = 0.044), respectively) were associated with "N status" in dMMR tumours. Conclusion: Whilst overall staging accuracy was similar between groups, incorrectly N staged dMMR tumours were more likely to be overstaged than pMMR tumours, risking inappropriate surgical or neoadjuvant treatment. We describe novel relationships between several inflam-matory markers and pathological "N status" in dMMR CC, which if integrated into routine practice may improve CT staging accuracy. Advances in knowledge: Compared to pMMR CC, dMMR CC is at significant risk of N overstaging. Platelet count, CRP and neutrophil count are higher in dMMR CC patients with nodal metastases than those without, and their role in refining clinical staging requires further investigation.