Nelmastobart（hSTC810） is a novel humanized monoclonal antibody that fuses on IgG4 and targets a novel immune checkpoint protein, BTN1A1+.This is an phase Ib bridging trial conducted in China to assess the safety, tolerability, and pharmacokinetic characteristics of Nelmastobart in combined with TAS-102 and Bevacizumab in Chinese participants with mCRC, and to verify that the safety results align with those from the Korean STCUBE-003 phase Ib trial. The phase Ib trial will also provide supportive data for conducting a randomized, double-blind, controlled Phase II study in China.