The study is being conducted to evaluate the efficacy, safety and tolerability of radiotherapy and chemotherapy, apatinib with camrelizumab in the neoadjuvant (prior to surgery) and adjuvant (after surgery) treatment of previously untreated adults with gastric and gastroesophageal junction (GEJ) adenocarcinoma.

Inclusion Criteria:

• Has previously untreated localized gastric or GEJ adenocarcinoma as defined by T3-4N+M0;
• Plans to proceed to surgery following pre-operative chemotherapy. Has an Eastern Cooperative Oncology Group (ECOG) performance status score of 0 to 1.
• Has adequate organ function.
• Male participants of childbearing potential must agree to use an adequate method of contraception for the course of the study through 120 days after the last dose of therapy.
• Female participants of childbearing potential must be willing to use an adequate method of contraception for the course of the study through 120 days after the last dose of therapy.
• Has life expectancy of greater than 12 months.

Exclusion Criteria:

• Uncontrolled hypertension ( systolic ≥140 mmHg or diastolic ≥90 mmHg despite antihypertensive therapy)
• Known hypersensitivity to any of the study drugs or excipients.
• Known hereditary or acquired bleeding and thrombotic tendencies (e.g. hemophiliacs, coagulation disorders, thrombocytopenia, etc.);
• Congenital or acquired immune deficiency (e.g. HIV infected)