Clinical Trial Evaluating FOLFIRI + Durvalumab vs FOLFIRI + Durvalumab and Tremelimumab in Second-line Treatment of Patients With Advanced Gastric or Gastro-oesophageal Junction Adenocarcinoma

* Age ≥ 18 years.

* Body weight > 30kg.

* Histologically proven advanced-stage unresectable adenocarcinoma of the stomach or the GEJ (Siewert II or III).

* Known MSS/MSI status or tumor tissue available (frozen or paraffin-embedded, primary tumors or metastases) in order to allow determination of MSS/MSI status. The investigator needs to ensure that tumor tissues will be sent after patient randomization.

* Failure to platinium-based 1st line therapy with or without trastuzumab, or early recurrent disease after surgery with neo-adjuvant and/or adjuvant platinium-based chemotherapy (within 6 months of the end of chemotherapy) or progression during neo-adjuvant and/or adjuvant platinium-based chemotherapy.

* Eligible for a second-line treatment with irinotecan and 5-FU.

* Measurable or non-measurable lesion according to the Response Evaluation Criteria in Solid Tumors (RECIST 1.1).

* Eastern Cooperative Oncology Group (ECOG) performance status 0-1.

* Adequate organ function: ANC ≥ 1.5 x 109/L, haemoglobin ≥ 9 g/dL, platelets ≥ 100 x 109/L, AST/ALT ≤ 3 x ULN (≤ 5 x ULN in case of liver metastase(s)), GGT ≤ 3 x ULN (≤ 5 x ULN in case of liver metastase(s)), bilirubin ≤ 1.5 x ULN, creatinin clearance > 40 mL/min (MDRD).

* Evidence of post-menopausal status or negative urinary or serum pregnancy test for female pre-menopausal patients.

* Man and woman who childbearing potential agrees to use two methods (one for the patient and one for the partner) of medically acceptable forms of contraception during the study and for 6 months after the last treatment intake.

* Patient is able to understand, sign, and date the written informed consent form at the screening visit prior to any protocol-specific procedures performed.

* - Concurrent enrolment in another clinical study - unless it is an observational study or during the follow-up period of an interventional study.

* Receipt of the last dose of anticancer therapy ≤ 2 weeks prior to the first dose of study drug.

* Radiotherapy within 4 weeks prior to the first dose of treatment.

* History of chronic inflammatory bowel disease (IBD).

* Current or prior bowel obstruction within 28 days before the first dose of study drugs.

* Any unresolved significant toxicity NCI CTCAE v4.0 ≥ grade 2 from previous anticancer therapy.

* Concurrent use of hormonal therapy for non-cancer-related conditions is acceptable

* Major surgical procedure (e.g. exploratory laparoscopy is not considered as a major surgical procedure) within 28 days prior to the first dose of treatment.

* Prior allogeneic bone marrow transplantation or prior solid organ transplantation.

* Active or prior documented autoimmune or inflammatory disorders (patients with alopecia, vitiligo, controlled hypo or hyperthyroidism, any chronic skin condition not requiring immunosuppressant therapy are eligible). Patients without active disease in the last 5 years may be included.

* Uncontrolled intercurrent illness, including but not limited to, ongoing or active infection, symptomatic congestive heart failure, uncontrolled hypertension, unstable angina pectoris, cardiac arrhythmia, interstitial lung disease, serious chronic gastrointestinal conditions associated with diarrhea, or psychiatric illness/social situations that would limit compliance with study requirement, substantially increase risk of incurring AEs or compromise the ability of the patient to give written informed consent.

* Severe cardiac disorders within 6 months.

* Severe liver dysfunction

* History of idiopathic pulmonary fibrosis, drug-induced pneumonitis, organizing pneumonia, or evidence of active pneumonitis on screening chest CT-scan.

* History of leptomeningeal carcinomatosis. Patients whose brain metastases have been treated may participate provided they show radiographic stability. In addition, any neurologic symptoms that developed either as a result of the brain metastases or their treatment must have resolved or be stable either, without the use of steroids, or are stable on a steroid dose of ≤10mg/day of prednisone or its equivalent for at least 14 days prior to the start of treatment

* Positive test for HIV, active hepatitis B or hepatitis C, active tuberculosis.

* History of active primary immunodeficiency

* Current or prior use of immunosuppressive medication within 14 days before the first dose of study drugs (excepted: intranasal, inhaled, topical steroids or local steroid injection -at physiologic dose does not exceed 10 mg/day of prednisone or its equivalent - steroids as premedication for hypersensitivity reactions).

* Receipt of live attenuated vaccine within 30 days prior to the first dose of treatment

* Known allergy or hypersensitivity to any of the study drugs or any of the study drug excipients. In order to check all the contraindications of each drugs, please refer to the updated versions of the SmPCs presented in Appendix 9.

* Current or prior use of St. John's Wort within 14 days before the first dose of study drugs (St. John's Wort is not allowed during participation in the trial).

* Treatment with sorivudine or analogs (brivudine).

* Treatment with phenytoin or analogs.

* Prior treatment with irinotecan, anti-PD1, anti PD-L1, anti-CLTA4 or other immunotherapy for cancer treatment

* Known Uridine Diphosphate Glucuronyltransferase (UGT1A1) or Dihydropyrimidine Dehydrogenase (DPD) enzyme deficiencies.

* Active infection requiring intravenous antibiotics at the time of Day 1 of Cycle 1.

* Other malignancy within 5 years prior to study enrolment, except for localized cancer in situ, basal or squamous cell skin cancer.

* Pregnant or breastfeeding female patient.