Breaching the immune-cold barrier in pMMR/MSS metastatic colorectal cancer: emerging strategies beyond standard care

Mismatch repair-proficient (pMMR) or microsatellite stable (MSS) metastatic colorectal cancer (mCRC) remains largely refractory to immunotherapy due to its intrinsically immunologically cold tumor microenvironment. Although frontline chemotherapy combined with immune-induction strategies can improve progression-free survival, these benefits have not translated into overall survival gains. Importantly, late-line trials such as LEAP-017 suggest that biologically meaningful immune activity may be masked by dilution effects in unselected populations. This review advocates a shift from empirical treatment approaches toward mechanism-driven precision stratification in refractory pMMR/MSS mCRC. We highlight two complementary immune activation strategies: tumor microenvironment remodeling via tyrosine kinase inhibitor-mediated vascular normalization, and intensified immune priming through cytotoxic T-lymphocyte-associated protein 4 blockade. To address persistently low response rates, we propose an integrated precision framework incorporating genomic repurposing, anatomical filtering, and multimodal synergy, aiming to translate transient immune activation into durable survival benefit.