A Phase II Study of Tegafur-Uracil as Maintenance Chemotherapy in Patients With Stage II Microsatellite-Stable or Low-Level Microsatellite-Instability Colon Cancer

Approximately 15% cases of colon cancer are associated a type of inherited susceptibility called defective DNA mismatch repair (MMR), which is frequently measured by either the presence of microsatellite instability (MSI) or by testing for loss of the protein products for genes involved in DNA MMR (MLH1, MSH2, MSH6 and PMS2). Tumors are classified according to the percentage of abnormal microsatellite regions present: >30-40% as high-level MSI (MSI-H), <30-40% as low-level MSI (MSI-L) and no abnormalities as microsatellite stable (MSS). In the condition of MSI presence, evidence shows that MSI is a marker of a more favorable survival outcome and a predictor of decreased benefit from adjuvant therapy with 5-FU in patients with stage II disease. MSI status can be used in the clinic as a prognostic tool to identify a subgroup of stage II patients with improved prognosis. Patients with MSI-H tumors are not suggested to have adjuvant chemotherapy while patients with MSI-L or MSS tumors can benefit from adjuvant chemotherapy. oral tegafur-uracil as an adjuvant chemotherapy in patients with Dukes' stage B2 and C2 colon cancer could be a good alternative to infusional 5-FU. Current evidences suggest adjuvant 5-FU-based therapy could improve survival outcome for patients with stage II MSI-L or MSS colon cancer, but not for patients with MSI-H colon cancer. Thus, oral tegafur-uracil is considered to have similar efficacy as 5-FU in this population.