This is a multicenter, open-label, prospective, randomized controlled Phase II clinical study. All eligible subjects will be randomly assigned in a 1:1 ratio to either the triple therapy group or the double therapy group. Triple therapy group: Subjects will receive Thymalfasin in combination with Regorafenib and Tislelizumab until iCPD is achieved per iRECIST (progressive disease (PD) per iRECIST), or until an intolerable toxicity occurs; Double therapy group: Subjects will receive Regorafenib and Tislelizumab until iCPD is achieved per iRECIST (PD per iRECIST), or until an intolerable toxicity occurs.

Assuming the following hypotheses: H0: The mPFS of the test group minus the mPFS of the control group equals 0 H1: The mPFS of the test group minus the mPFS of the control group does not equal 0 Assuming an mPFS of 5.0 months for the test group and 1.8 months for the control group, with a two-sided alpha level of 0.05 and 80% power, at least 32 events need to be observed. Within a 9-month enrollment period and a total study duration of 15 months, 44 subjects need to be enrolled to achieve this. Considering an additional dropout rate of 15%, 26 subjects per group are required, totaling 52 subjects (using PASS 2023 Log-rank procedure). Enrollment sites: Beijing Friendship Hospital, Capital Medical University, Peking Union Medical College Hospital, Peking University People's Hospital. Allocation of enrollment across sites: Each site will compete for enrollment, with each site enrolling no less than 14 subjects. 1. Regorafenib: Start at 80 mg once daily, orally, taken at a fixed time for 2 consecutive weeks and then stopped for 1 week. If the patient tolerates it well, increase to 120 mg/d in Cycle 2. 2. Tislelizumab: 200 mg, iv.gtt, single infusion, 21 days as a cycle, Day 1. 3. Thymalfasin: 4.8 mg, administered subcutaneously twice weekly. Treatment will continue until disease progression or until an intolerable adverse reaction occurs that does not resolve despite dose modification.