Inclusion Criteria:

          -  Subjects must have signed and dated an Institutional Review Board (IRB)/Independent
             Ethics Committee (IEC) approved written informed consent form in accordance with
             regulatory and institutional guidelines. This must be obtained before the performance
             of any protocol-related procedures that are not part of normal subject care. Subjects
             must be willing and able to comply with scheduled visits, treatment schedule,
             laboratory tests and other requirements of the study.

          -  All subjects must have localized/eligible for surgery gastric cancer (GC) or GEJ
             carcinoma type III, with negative peritoneal washing. Subjects must have
             histologically confirmed predominant adenocarcinoma. The documentation of GEJ
             involvement can include biopsy, endoscopy, or imaging.

          -  Subject must be previously untreated with systemic treatment (including HER 2
             inhibitors) given as primary therapy for advanced or metastatic disease. No prior
             neoadjuvant chemotherapy, immunotherapy, radiotherapy and/or chemoradiotherapy are
             permitted.

          -  Eastern Cooperative Oncology Group (ECOG) performance status score of 0 or 1.

          -  Absolute neutrophil count (ANC) >= 1,500/mcL (within 28 days of treatment initiation).

          -  Platelets >=100,000/mcL (within 28 days of treatment initiation).

          -  Hemoglobin >= 9 g/dL or > 5.6 mmol/L; if patient is not actively bleeding and has
             hemoglobin of < 9g/dL, patient can receive blood transfusion to increase hemoglobin to
             >= 9g/dL (within 28 days of treatment initiation).

          -  Serum creatinine =< 1.5 X upper limit of normal (ULN) OR measured or calculated
             creatinine clearance (glomerular filtration rate [GFR] can also be used in place of
             creatinine or creatinine clearance [CrCL]) > 60 mL/min for subjects with creatinine
             levels > 1.5 x institutional ULN (measured via 24-hour urine collection) (within 28
             days of treatment initiation). Creatinine clearance should be calculated per
             institutional standard.

          -  Serum total bilirubin =< 1.5 X ULN (1.5 mg/dL or 25.65 umol/L) OR direct bilirubin <
             ULN for subjects with total bilirubin levels < 1.5 X ULN. Except patients with
             Gilbert's disease (< 3 X ULN) (within 28 days of treatment initiation).

          -  Aspartate aminotransferase AST (serum glutamic oxaloacetic transaminase [SGOT]) and
             alanine aminotransferase (ALT) (serum glutamate pyruvate transaminase [SGPT]) =< 2.5 X
             ULN OR < 5 X ULN for subjects with liver metastases (within 28 days of treatment
             initiation).

          -  Albumin >= 3 mg/dL (within 28 days of treatment initiation).

          -  Prothrombin Time (PT) < 1.5 X ULN unless subject is receiving anticoagulant therapy as
             long as PT or partial thromboplastin time PTT is within therapeutic range of intended
             use of anticoagulants. Activated partial thromboplastin Time (aPTT) < 1.5 X ULN unless
             subject is receiving anticoagulant therapy as long as PT or PTT is within therapeutic
             range of intended use of anticoagulants (within 28 days of treatment initiation).

          -  Women of childbearing potential (WOCBP) must have a negative serum or urine pregnancy
             test (minimum sensitivity 25 IU/L or equivalent units of human chorionic gonadotropin
             [HCG]) within 24 hours prior to the start of study drug. Women must not be
             breastfeeding.

          -  Prior to chemotherapy and immunotherapy, WOCBP must agree to follow instructions for
             method(s) of contraception for the duration of study treatment with nivolumab and 5
             months after the last dose of study treatment (i.e. 30 days (duration of ovulatory
             cycle plus the time required for the investigational drug to undergo approximately
             five half-lives).

          -  Males who are sexually active with WOCBP must agree to follow instructions for methods
             of contraception for the duration of study treatment with nivolumab and 7 months after
             the last dose of study treatment (i.e. 90 days (duration of sperm turnover) plus the
             time required for the investigational drug to undergo approximately five half-lives).
             In addition, male subjects must be willing to refrain from sperm donation during this
             time.

        Exclusion Criteria:

          -  Participants with an active, known or suspected autoimmune disease. Participants with
             type I diabetes mellitus, hypothyroidism only requiring hormone replacement, skin
             disorders (such as vitiligo, psoriasis, or alopecia) not requiring systemic treatment,
             or conditions not expected to recur in the absence of an external trigger are
             permitted to enroll.

          -  Participants with a condition requiring systemic treatment with either corticosteroids
             (> 10 mg daily prednisone equivalent) or other immunosuppressive medications within 14
             days of study treatment. Inhaled or topical steroids, and adrenal replacement steroid
             doses > 10 mg daily prednisone equivalent, are permitted in the absence of active
             autoimmune disease.

          -  Known history of positive test for human immunodeficiency virus (HIV) or known
             acquired immunodeficiency syndrome (AIDS).

               -  NOTE: Testing for HIV must be performed at sites where mandated locally.

          -  White blood cell (WBC) < 2000/uL.

          -  Any positive test result for hepatitis B virus or hepatitis C virus indicating
             presence of virus, e.g. hepatitis B surface antigen (HBsAg Australia antigen)
             positive, or hepatitis C antibody (anti-HCV) positive (except if hepatitis C virus-
             ribonucleic acid [HCV-RNA] negative).

          -  History of allergy or hypersensitivity to study drug components.

          -  Prior malignancy active within the previous 3 years except for locally curable cancers
             that have been apparently cured, such as basal or squamous cell skin cancer,
             superficial bladder cancer, or carcinoma in situ of the prostate, cervix, or breast.

          -  Patients with serious or uncontrolled medical disorders.

          -  Prior treatment with an anti-PD-1, anti-PD-L1, anti-PD-L2, or anti-CTLA-4 antibody, or
             any other antibody or drug specifically targeting T-cell co-stimulation or checkpoint
             pathways.