Harbour BioMed (HBM Holdings Ltd.) has announced positive results from a Phase II clinical study evaluating porustobart (HBM4003), a next-generation, fully human heavy-chain-only anti-CTLA-4 antibody, in combination with tislelizumab for patients with microsatellite stable $(MSS)$ metastatic colorectal cancer (mCRC). The multicenter, open-label trial enrolled 24 heavily pretreated patients with non-liver-metastatic MSS mCRC. Patients received HBM4003 and tislelizumab every 21 days. Among 23 evaluable patients, the objective response rate $(ORR)$ was 34.8%, with eight partial responses. The disease control rate (DCR) was 60.9%, and the median progression-free survival (mPFS) was 4.2 months. The most common treatment-related adverse events were liver function test abnormalities, hematological abnormalities, and pyrexia, mostly Grade 1-2. Serious adverse events related to treatment occurred in 37.5% of patients, with no Grade 4 or fatal events reported. The results have already been announced by the company.