 In this study, participants with advanced or metastatic adenocarcinoma or squamous cell carcinoma of the esophagus or Siewert type I adenocarcinoma of the esophagogastric junction EGJ that has progressed after first-line standard therapy will be randomized to receive either single agent pembrolizumab or the Investigators choice of standard therapy with paclitaxel, docetaxel, or irinotecan. The primary study hypothesis is that treatment with pembrolizumab will prolong overall survival OS as compared to treatment with standard therapy. 