Pressurized Intraperitoneal Aerosol Chemotherapy (PIPAC) With Oxaliplatin In Patients With Peritoneal Carcinomatosis

Inclusion Criteria for Cohort 1:

* Gastric cancer patients with peritoneal metastasis on peritoneal cytology/histology.
* Patients who refuse, are unable to tolerate, or have completed at least 1st line systemic chemotherapy.
* Patients who have completed chemotherapy/targeted therapy \> 21 days or at least 5 half-lives (or whichever is longer) prior to PIPAC.
* Age \>21 years.
* Eastern Cooperative Oncology Group performance status 0-1.
* Adequate bone marrow function (neutrophil count \>1500/mm3, hemoglobin \>8.0 g/dl and platelet count \>100 000/mm3).
* Adequate liver function (bilirubin, AST/ALT within upper limit of normal)
* Adequate renal function (serum creatinine within the upper limit of normal)
* Expected survival \>3 months
* Women of child-bearing potential and men must agree to use adequate contraception prior to study entry and for the duration of study participation.

Exclusion Criteria for Cohort 1:

* Predominant extra-peritoneal metastases at the discretion of the study team after discussion at the multidisciplinary tumour board
* Good response to systemic chemotherapy based on RECIST guidelines VI.I with complete or partial response to systemic chemotherapy.
* Known allergy to oxaliplatin
* Previous malignancy unrelated to current peritoneal carcinomatosis diagnosed in the last 5 years
* Patients with treated skin cancer besides melanoma may be included.
* Patients with reproductive potential who refuse to use an adequate means of contraception (including male patients)
* Significant disease or conditions which, in the investigator's opinion, would exclude patient from the study
* Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements
* Pregnant or lactating female

Inclusion Criteria for Cohort 2:

* Gastric cancer patients with peritoneal metastasis on peritoneal cytology/histology, for whom oxaliplatin is considered standard of care for the peritoneal carcinoma of origin.
* Patients who refuse, are unable to tolerate, or have completed at least 1st line systemic chemotherapy
* Patients who have completed chemotherapy/targeted therapy \> 21 days or at least 5 half-lives (or whichever is longer) prior to PIPAC
* Patients must have recovered (≤ grade 1) from all reversible treatment toxicity from prior chemotherapy, radiotherapy or surgery.
* Age ≥21 years
* Eastern Cooperative Oncology Group performance status 0-1
* Adequate bone marrow function (neutrophil count ≥1500/mm3, hemoglobin ≥8.0 g/dl and platelet count ≥100 000/mm3)
* Adequate liver function (bilirubin ≤ 1.5x ULN(upper limit normal) and AST/ALT ≤3x ULN or ≤5x ULN in the presence of liver metastases)
* Adequate renal function (serum creatinine ≤1.5x ULN)
* Expected survival \>3 months
* Women of child-bearing potential and men must agree to use adequate contraception prior to study entry and for the duration of study participation.

Exclusion Criteria for Cohort 2:

* Predominant extra-peritoneal metastases at the discretion of the study team after discussion at the multidisciplinary tumour board
* Patients who have previously received prior nivolumab or PD-/L1 blockade therapy
* Patients with clinical or radiological evidence of hollow viscera perforation or impending perforation, including but not limited to gastric, small bowel, colon, gallbladder. Decision will be made at the discretion of the study team in consultation with multidisciplinary tumour board or with necessary specialists
* Good response to systemic chemotherapy based on RECIST guidelines VI.I with complete or partial response to systemic chemotherapy.
* Active autoimmune disease requiring disease-modifying therapy.
* Concurrent systemic steroid therapy higher than physiologic dose (equivalent of prednisolone 10mg daily), except for short courses (\< 2 weeks) required to treat acute medical conditions (e.g. asthma exacerbation, or for CT scans)
* Any form of active primary or secondary immunodeficiency.
* Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, uncontrolled hypertension (systolic \>160 mmHg and/or diastolic \>100 mmHg), symptomatic congestive heart failure, unstable angina pectoris, myocardial infarction/cerebrovascular event (≤ 6 months prior to study entry), cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements, long term systemic immunosuppressant or corticosteroid, and active viral hepatitis.
* Known allergy to oxaliplatin
* Previous malignancy unrelated to current peritoneal carcinomatosis diagnosed in the last 2 years
* Patients with treated skin cancer besides melanoma may be included.
* Patients with reproductive potential who refuse to use an adequate means of contraception (including male patients)
* Significant disease or conditions which, in the investigator's opinion, would exclude patient from the study
* Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements
* Pregnant or lactating female