 In this study, participants with MSI-H or dMMR advanced colorectal carcinoma will be randomly assigned to receive either pembrolizumab or the Investigators choice of 1 of 6 standard of care SOC chemotherapy regimens for the treatment of advanced colorectal carcinoma. The primary study hypothesis is that pembrolizumab will prolong progression-free survival PFS or overall survival OS compared to current SOC chemotherapy. 