Study of Pembrolizumab (MK-3475) in Previously-Treated Participants With Advanced Carcinoma of the Esophagus or Esophagogastric Junction (MK-3475-180/KEYNOTE-180)

Inclusion Criteria:

* Has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
* Life expectancy greater than 3 months
* Histologically-proven advanced/metastatic adenocarcinoma or squamous cell carcinoma of the esophagus or advanced/metastatic Siewert type 1 adenocarcinoma of the EGJ
* Documented objective radiographic or clinical disease progression on two previous lines of standard therapy
* Measurable disease based on Response Evaluation Criteria In Solid Tumors (RECIST) 1.1
* Can provide either a newly obtained or archival tumor tissue sample for intratumoral immune-related testing and for anti-programmed cell death (PD-1)
* Female participants of childbearing potential must be willing to use adequate contraception for the course of the study through 120 days after the last dose of study medication
* Male participants must agree to use adequate contraception starting with the first dose through 120 days after the last dose of study medication
* 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
* Has active autoimmune disease that has required systemic treatment within the 2 years prior to the first dose of study medication
* 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
* Prior anti-cancer mAb, chemotherapy, targeted small molecule therapy, or radiation therapy within 2 weeks prior to first dose of study medication or not recovered from adverse events due to a previously administered agent
* Prior therapy with an anti-PD-1, anti-PD-Ligand 1 (PD-L1), or anti-PD-L2 agent, or previously participated in a 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 basal cell carcinoma of the skin, squamous cell carcinoma of the skin that has undergone potentially curative therapy, in-situ cervical cancer, 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 active Hepatitis B or C
* 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 study medication