Colorectal cancers (CRCs) with deficient DNA mismatch repair (MMR) system (so called dMMR or MSI tumors) represent a no-negligible part of sporadic CRCs. Prognostic value of this unique cell population remains controversial, but undoubtedly these tumors are characterized by poor response to conventional chemotherapy, an high tumor mutational burden resulting in a brisk immuno response, and, as recently observed, excellent results to the immunotherapy. The aim of this study was to evaluate, by using sophisticated statistical analyses, the predictive value of MSI status and its optimal treatment.~A series of 403 consecutive CRC patients treated by the same oncological team from 2014 to 2021 entered the study. No patients underwent immunotherapy. Immunohistochemistry, integrated by polymerase chain reaction if appropriate, was used to categorize specimens in microsatellite stable (MSS) and instable (MSI) tumors. The win ratio (WR) approach was utilized to compare composite outcomes of MSS and MSI tumors while controlling for radical versus no radical resection, propensity score-matched analysis, and reversing primary endpoint.
Microsatellite instable (MSI) tumors represent almost the 15% of all sporadic colorectal cancers (CRCs).~Literature data show that this unique tumor population appears to be poorly responsive to conventional chemotherapy and conversely reveals excellent results to immunotherapy.~Our data, as demonstrated by propensity score-matched and win ratio analysis, show that there are no substantial differences between MSI and MSS tumors in early CRC stages treated with surgery alone.~On the contrary, stable tumors (MSS) did much better than MSI tumors in advanced CRC stages undergoing conventional adjuvant treatment.~Determination of status of DNA mismatch repair system is crucial in high-risk CRCs to optimize treatment.