Tislelizumab Combined With Apatinib and Oxaliplatin Plus S1 Vs Oxaliplatin Plus S1 as Neoadjuvant Therapy for Borrmann IV、Large Borrmann III Type and Bulky N Positive Advanced Gastric Cancer

Participants will receive Tislelizumab, 200mg, intravenously over 30 - 60 minutes, day 1 of every 3 weeks for 4 cycles. Discontinuation will be considered due to toxicity, withdrawal of consent, or end of study. Every 3-week treatment period was considered to be a cycle.

Participants will receive apatinib, 250mg, qd，every 3 weeks for 3 weeks

Participants will receive oxaliplatin, 130mg/m2, day 1 of every 3 weeks for 4 weeks.

Participants will receive S-1, day 1-14 of every 3 weeks for 4 weeks.