Cancer Genetics and Epigenetics, 2025, Vol.13, No.6, 300-309 http://medscipublisher.com/index.php/cge 303 predictor because some patients with low or no PD-L1 expression can still benefit from ICIs treatment, which indicates that other biomarkers are still needed as supplements. Figure 1 Overall Survival in the Intention-to-Treat Population (Adopted from Rini et al., 2019) Tumor mutational burden (TMB), microsatellite instability (MSI), or mismatch repair deficiency (dMMR) are also regarded as important factors in predicting the efficacy of immunotherapy. High TMB usually indicates that more neoantigens are produced in the tumor, which are more easily recognized by the immune system and thus have a better response to ICIs. Similarly, tumors of MSI-H or dMMR, such as certain colorectal cancers and endometrial cancers, respond significantly to PD-1 inhibitors. Therefore, the FDA approved pembrolizumab for all patients with MSI-H/dMMR tumors, regardless of their primary site. 4.2 Tumor microenvironment and degree of immune cell infiltration The tumor microenvironment has an important influence on the therapeutic effect of ICIs. If the tumor microenvironment is "hot", that is, contains a large number of cytotoxic T cells, then the patient's response to immunotherapy is usually better. On the contrary, patients with "cold" tumors who have few immune cells or a large number of immunosuppressive cells (such as regulatory T cells and myeloid-derived suppressor cells) are often insensitive to ICIs (Binnewies et al., 2018; Wang, 2025).
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