The study of mismatch repair [MMR] genes and clinicopathological risk factors in treatment of stage-II colon cancer: Preliminary report of 2-year follow-up at Chulabhorn Hospital

Background: Early-stage colon cancer is increasingly detected by colonoscopic screening. The development of adjuvant chemotherapy in patients with stage-II colon cancer remains a challenge. In Thailand, the clinicopathological risk factors [CPR] are currently used as criteria for the selection of adjuvant chemotherapy in each patient. Previous reports showed that mismatch repair gene [MMR] status could be a prognostic factor for the decision on adjuvant chemotherapy. Objective: To determine the characteristics of MMR status and CPR of Thai colon cancer cases, with treatment follow-up in stage-II colon cancer by MMR and CPR. Materials and Methods: This was a preliminary report of patients with stage-II colon cancer who received treatment at Chulabhorn Hospital. MMR status was determined by microsatellite instability [MSI] testing and CPR was determined in each patient. Patients with deficient MMR and low CPR received post-surgery surveillance whereas those with proficient MMR and/or high CPR were treated with adjuvant chemotherapy (5-FU/LV). The follow-up of adverse events, serious adverse events, disease-free survival [DFS], and overall survival [OS] was at the third and fifth years. Results: During July 4,2014 to December 31,2016, there were 31 cases of stage-II colon cancer. All of them were at the stage of T3NoMo (IIA). High CPR and low CPR were found in 20 cases (64.52%) and 11 cases (35.48%), respectively. There were 28 cases with MMR testing results. Proficient MMR (MSI-low) was observed in 23 cases (82.14%). There were 3 cases with disease recurrence, all of which were in proficient MMR group and received adjuvant chemotherapy. Serious adverse events were found in 2 cases with infection during febrile neutropenia after chemotherapy but no treatment-related death was observed. DFS and OS could not yet be evaluated. Conclusion: Incidence of proficient MMR (MSI-low) in Thai patients with stage-II colon cancer was comparable to that of other countries (80 to 90%). Treatment by adjuvant chemotherapy using MMR status and CPR was feasible with low serious adverse events.