The role of chemotherapy in microsatellite unstable (MSI-H) colorectal cancer

Introduction High-frequency microsatellite instability (MSI-H) is an alternate pathway of colorectal carcinogenesis, which accounts for 15% of all sporadic colorectal cancers. These tumours arise from mutations in the DNA mismatch repair system and thus have different responses to chemotherapeutic agents compared to inicrosatellite stable (MSS) cancers. Objective This review aims to summarise the available literature on the responses to chemotherapy in MSI-H colorectal cancer (CRC). Results and discussion 5 Fluorouracil (5FU) is commonly used as a chemotherapeutic agent in colon cancer and in vitro evidence shows reduced response to 5FU in MSI-H CRC. The clinical evidence is conflicting but favours a reduced response to 5FU in MSI-H CRC. Several newer agents such as COX-2 inhibitors and irinotecan are also reviewed. Conclusion Available evidence suggests that MSI-H CRC have different behaviour pattems and response to chemotherapy compared with MSS CRC.