• Overall Survival (OS) in All Participants [ Time Frame: From randomization through final analysis data cutoff date of 13-Feb-2019 (Up to approximately 24 months) ]
  OS was defined as the time from randomization to death due to any cause. Median OS in all participants is presented.
• Overall Survival (OS) in Participants With Programmed Death-Ligand 1 Combined Positive Score ≥10 (PD-L1 CPS ≥10) [ Time Frame: From randomization through final analysis data cutoff date of 13-Feb-2019 (Up to approximately 24 months) ]
  OS was defined as the time from randomization to death due to any cause. Median OS in participants with a PD-L1 CPS ≥10 is presented.
• Overall Survival (OS) in Participants With Squamous Cell Carcinoma (SCC) of the Esophagus [ Time Frame: From randomization through final analysis data cutoff date of 13-Feb-2019 (Up to approximately 24 months) ]
  OS was defined as the time from randomization to death due to any cause. Median OS in participants with SCC of the esophagus is presented.

• Objective Response Rate (ORR) as Assessed by Response Evaluation Criteria in Solid Tumors Version 1.1 (RECIST 1.1) in All Participants [ Time Frame: From randomization through final analysis data cutoff date of 13-Feb-2019 (Up to approximately 24 months) ]
  ORR was defined as the percentage of participants who had a Complete Response (CR: Disappearance of all target lesions) or a Partial Response (PR: ≥30% decrease in the sum of diameters of target lesions) as assessed using RECIST 1.1 by central imaging vendor review. The percentage of all participants who experienced a CR or PR is presented.
• Objective Response Rate (ORR) as Assessed by Response Evaluation Criteria in Solid Tumors Version 1.1 (RECIST 1.1) in Participants With Programmed Death-Ligand 1 Combined Positive Score ≥10 (PD-L1 CPS ≥10) [ Time Frame: From randomization through final analysis data cutoff date of 13-Feb-2019 (Up to approximately 24 months) ]
  ORR was defined as the percentage of participants who had a Complete Response (CR: Disappearance of all target lesions) or a Partial Response (PR: ≥30% decrease in the sum of diameters of target lesions) as assessed using RECIST 1.1 by central imaging vendor review. The percentage of participants with a PD-L1 CPS ≥10 who experienced a CR or PR is presented.
• Objective Response Rate (ORR) as Assessed by Response Evaluation Criteria in Solid Tumors Version 1.1 (RECIST 1.1) in Participants With Squamous Cell Carcinoma (SCC) of the Esophagus [ Time Frame: From randomization through final analysis data cutoff date of 13-Feb-2019 (Up to approximately 24 months) ]
  ORR was defined as the percentage of participants who had a Complete Response (CR: Disappearance of all target lesions) or a Partial Response (PR: ≥30% decrease in the sum of diameters of target lesions) as assessed using RECIST 1.1 by central imaging vendor review. The percentage of participants with SCC of the esophagus who experienced a CR or PR is presented.
• Progression-free Survival (PFS) as Assessed by Response Evaluation Criteria in Solid Tumors Version 1.1 (RECIST 1.1) in All Participants [ Time Frame: From randomization through final analysis data cutoff date of 13-Feb-2019 (Up to approximately 24 months) ]
  PFS was defined as the time from randomization to the first documented progressive disease (PD) or death due to any cause, whichever occurred first. Per RECIST 1.1, PD was defined as ≥20% increase in the sum of diameters of target lesions. In addition to the relative increase of 20%, the sum must also have demonstrated an absolute increase of ≥5 mm. The appearance of ≥1 new lesions was also considered PD. Median PFS as assessed by central imaging vendor review per RECIST 1.1 in all participants is presented.
• Progression-free Survival (PFS) as Assessed by Response Evaluation Criteria in Solid Tumors Version 1.1 (RECIST 1.1) in Participants With Programmed Death-Ligand 1 Combined Positive Score ≥10 (PD-L1 CPS ≥10) [ Time Frame: From randomization through final analysis data cutoff date of 13-Feb-2019 (Up to approximately 24 months) ]
  PFS was defined as the time from randomization to the first documented progressive disease (PD) or death due to any cause, whichever occurred first. Per RECIST 1.1, PD was defined as ≥20% increase in the sum of diameters of target lesions. In addition to the relative increase of 20%, the sum must also have demonstrated an absolute increase of ≥5 mm. The appearance of ≥1 new lesions was also considered PD. Median PFS as assessed by central imaging vendor review per RECIST 1.1 is presented for participants with a PD-L1 CPS ≥10.
• Progression-free Survival (PFS) as Assessed by Response Evaluation Criteria in Solid Tumors Version 1.1 (RECIST 1.1) in Participants With Squamous Cell Carcinoma (SCC) of the Esophagus [ Time Frame: From randomization through final analysis data cutoff date of 13-Feb-2019 (Up to approximately 24 months) ]
  PFS was defined as the time from randomization to the first documented progressive disease (PD) or death due to any cause, whichever occurred first. Per RECIST 1.1, PD was defined as ≥20% increase in the sum of diameters of target lesions. In addition to the relative increase of 20%, the sum must also have demonstrated an absolute increase of ≥5 mm. The appearance of ≥1 new lesions was also considered PD. Median PFS as assessed by central imaging vendor review per RECIST 1.1 is presented for participants with SCC of the esophagus.
• Number of Participants Experiencing an Adverse Event (AE) [ Time Frame: From first dose of study treatment through end-of-trial analysis data cutoff date of 31-Dec-2021 (Up to approximately 5 years) ]
  An AE was defined as any untoward medical occurrence in a participant administered a study treatment and which does not necessarily have to have a causal relationship with this treatment. The number of participants who experienced ≥1 AE will be presented.
• Number of Participants Discontinuing Study Treatment Due an Adverse Event (AE) [ Time Frame: From first dose of study treatment through to end-of-trial analysis data cutoff date of 31-Dec-2021 (Up to approximately 5 years) ]
  An AE was defined as any untoward medical occurrence in a participant administered a study treatment and which does not necessarily have to have a causal relationship with this treatment. The number of participants who discontinued study treatment due to an AE will be presented.

• Objective Response Rate (ORR) [ Time Frame: Up to 5 years ]
• Progression-free Survival (PFS) [ Time Frame: Up to 5 years ]

In the China extension study, Chinese 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 Investigator's choice of chemotherapy with paclitaxel, docetaxel, or irinotecan.

The primary extension study hypothesis is that treatment with pembrolizumab will prolong overall survival (OS) as compared to treatment with chemotherapy.

• Esophageal Carcinoma
• Esophagogastric Junction Carcinoma

• Biological: pembrolizumab
  IV infusion
  Other Names:

  • KEYTRUDA®
  • MK-3475
• Drug: paclitaxel
  IV infusion
  Other Name: TAXOL®
• Drug: docetaxel
  IV infusion
  Other Name: TAXOTERE®
• Drug: irinotecan
  IV infusion
  Other Name: CAMPTOSAR®

• Experimental: Pembrolizumab
  Participants receive pembrolizumab 200 mg intravenously (IV) on Day 1 of every 21-day (3-week) cycle for up to 35 administrations (up to approximately 2 years).
  Intervention: Biological: pembrolizumab
• Active Comparator: Chemotherapy
  Participants receive Investigator's choice of chemotherapy: paclitaxel 80-100 mg/m^2 IV on Days 1, 8, and 15 of every 28-day (4-week) cycle, OR docetaxel 75 mg/m^2 IV on Day 1 of every 21-day (3-week) cycle, OR irinotecan 180 mg/m^2 IV on Day 1 of every 14-day (2-week) cycle (up to approximately 2 years).
  Interventions:

  • Drug: paclitaxel
  • Drug: docetaxel
  • Drug: irinotecan

Inclusion Criteria:

• Histologically- or cytologically-confirmed diagnosis of adenocarcinoma or squamous cell carcinoma of the esophagus or Siewert type I adenocarcinoma of the EGJ
• Metastatic disease or locally advanced, unresectable disease
• Life expectancy of greater than 3 months
• Measurable disease based on Response Evaluation Criteria In Solid Tumors (RECIST) 1.1
• Performance status of 0 or 1 on the Eastern Cooperative Oncology Group (ECOG) Performance Scale
• Documented radiographic or clinical disease progression on no more or less than one previous line of standard therapy
• Can provide either a newly obtained or archival tumor tissue sample for intra-tumoral immune-related testing and for anti-programmed cell death (PD)-1
• Participants of reproductive potential must be willing to use adequate contraception for the course of the study through 120 days after the last dose of pembrolizumab or through 180 days after the last dose of paclitaxel, docetaxel or irinotecan
• Adequate organ function

Exclusion Criteria:

• Currently participating and receiving study therapy or has participated in a study of an investigational agent and received study therapy or used an investigational device within 4 weeks of the first dose of study medication
• Active autoimmune disease that has required systemic treatment in past 2 years
• Diagnosis of immunodeficiency or receiving systemic steroid therapy or any other form of immunosuppressive therapy within 7 days prior to the first dose of study medication
• Known central nervous system (CNS) metastases and/or carcinomatous meningitis (includes past history or current metastasis)
• Has received prior anti-cancer monoclonal antibody (mAb), chemotherapy, targeted small molecule therapy, or radiation therapy within 2 weeks prior to study Day 1 or not recovered from adverse events due to a previously administered agent
• Has had a severe hypersensitivity reaction to treatment with another mAb
• Prior therapy with a PD-1, anti-PD-Ligand 1 (PD-L1), or anti-PD-L2 agent, or previously participated in Merck pembrolizumab (MK-3475) study
• Has a known additional malignancy that has progressed or required active treatment within the last 5 years with the exception of curatively treated basal cell and squamous cell carcinoma of the skin and/or curatively resected in-situ cervical and/or breast cancers, and in-situ or intra-mucosal pharyngeal cancer
• Received a live vaccine within 30 days of the first dose of study medication
• Known history of Human Immunodeficiency Virus (HIV) infection
• Known history of or is positive for hepatitis B (hepatitis B surface antigen reactive) or known active hepatitis C (hepatitis C virus RNA or hepatitis C antibody is detected)
• History of non-infectious pneumonitis that required steroids or current pneumonitis
• Active infection requiring systemic therapy
• Known psychiatric or substance abuse disorders that would interfere with cooperation with the requirements of the study
• Pregnant, breastfeeding, or expecting to conceive or father children within the projected duration of the study starting with the screening visit through 120 days after the last dose of pembrolizumab or through 180 days after the last dose of paclitaxel, docetaxel or irinotecan
• Known allergy, hypersensitivity, or contraindication to paclitaxel, docetaxel, or irinotecan or any components used in their preparation
• Experienced weight loss > 10% over approximately 2 months prior to first dose of study therapy
• Has ascites or pleural effusion by physical exam
• Has experienced documented objective radiographic or clinical disease progression during or after receiving more than 1 line of therapy.