Recently, pembrolizumab have been approved for advanced solid tumor with microsatellite instability-high, and nivolumab including combination therapy with ipilimumab for colorectal cancer with microsatellite instability-high, and usefulness of those 3 checkpoint inhibitors have been paid attention. Genetic testing is essential for selecting molecular-targeted drugs in colorectal cancer; however, the type of tests and their optimal timing are becoming more complicated. Hence, this article reviews the gene mutation tests used for advanced colorectal cancer, the molecular mechanism of colorectal cancer with microsatellite instability-high, the clinical development status of immune checkpoint inhibitors, and the future perspective on treatment strategy.