Results of ctDNA suggested the presence of TP53 p.S12F KRAS p.G12D mutations, TMB 2.51 Mut/MB (low)...the patient has received 19 cycles of combination therapy of tislelizumab and irinotecan and three cycles of tislelizumab maintenance therapy...the patient responded well to immunotherapy combined with chemotherapy for 17 months, and the response is still ongoing.