• Unresectable or advanced recurrent gastric cancer with evident peritoneal dissemination on imaging, or with ascites, as well as unresectable or advanced recurrent pancreatic cancer.

• Refractory/intolerant to more than 3 regimens of therapy for gastric cancer (more than 2 regimens acceptable for Phase II) or more than 2 regimens of therapy for pancreatic cancer (more than 1 regimen acceptable for Phase II)

• Abdominal port placement is possible

• No medical history of serious side effects or allergic reactions to pembrolizumab (only for patients in the pembrolizumab combination cohort)

• Diagnosed gastric adenocarcinoma or pancreatic cancer with by histological or cytological examination

• The patient has been confirmed to be negative (not MSS = MSI-high) by microsatellite instability (MSI) testing, or proficient mismatch repair (pMMR) by mismatch repair protein immunohistochemistry testing

• Eastern Cooperative Oncology Group (ECOG) Performance status(PS) 0-2

• Patient aged 20years or older

• Adequate major organs (bone marrow, heart, lungs, liver, kidneys, etc.) function:

‣ Neutrophil \>1,500/mm3

⁃ hemoglobin \>=8.0 g/dL

⁃ Platelet \>75,000/mm3

⁃ PT-INR \<1.5

⁃ AST, ALT \<=3 times the upper limit of reference value

⁃ T-Bil \<=2 times the upper limit of reference value (T-Bil \<=3.0mg/dL , when drainage for obstructive jaundice)

⁃ eGFR \>=30mL/min/1.73m2

⁃ Expected to survive for 3 months or more at the enrollment

⁃ Written informed consent