[Predictive and prognostic value of MSI phenotype in adjuvant colon cancer: Who and how to treat?]

The MSI phenotype in colon cancer is a good prognostic factor, with an impact probably more pronounced for stage II than stage III tumor. This survival advantage may be related to the tumor-infiltrating lymphocytes observed in MSI tumors, thus explaining the existence of a probably more effective anti-tumor immune response. In addition, the MSI status would also be a biomarker able to predict the lack of efficacy of adjuvant 5-fluorouracil (5FU) chemotherapy. In contrast, as observed in MSS colon cancer, the MSI tumors would have a survival benefit with the addition of oxaliplatin to adjuvant 5FU chemotherapy. Based on these data, the "French National Thesaurus of Digestive Oncology" suggests for patients with MSI colon cancer, an adjuvant chemotherapy combining fluoropyrimidine and oxaliplatin for stage III, and surgery alone without adjuvant chemotherapy for stage II (excepted for pT4b tumors in which the combination of fluoropyrimidine and oxaliplatin may be a therapeutic option). Beyond these recommendations, the discussion of adjuvant treatment in MSI tumors should also include other factors such as the patient's age and comorbidities. The duration of the adjuvant treatment (3 or 6 months) and the regimen used (FOLFOX or XELOX) should be based on the recommendations of the international IDEA consortium pending the results of the translational studies of this trial. Finally, the promising results of immunotherapy in metastatic MSI colorectal led to the development of clinical trials evaluating "immune checkpoint blockers" in combination with FOLFOX in the treatment of stage III MSI colon cancer.