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

• Phase I:

• Patients with gastric cancer who have received 3 or more prior chemotherapy regimens and are refractory or intolerant to these therapies, and patients with pancreatic cancer who have received 2 or more prior chemotherapy regimens and are refractory or intolerant to these therapies.

• Phase II:

• Patients with gastric cancer who have received 2 or more prior chemotherapy regimens, including at least 1 regimen containing an immune checkpoint inhibitor, and are refractory or intolerant to these therapies, and patients with pancreatic cancer who have received 1 or more prior chemotherapy regimens and are refractory or intolerant to these therapies.

• 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

• The Eastern Cooperative Oncology Group (ECOG) performance status(PS) at the time of informed consent meets the following conditions.

‣ Phase I ：0-2

⁃ Phase II ：0-1

• 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