Emerging evidence reveals the tumor suppressor gene CHEK2 not only functions in DNA repair but also modulates anti-tumor immunity in solid cancers. CHEK2 deficiency disrupts homologous recombination, elevates tumor mutation burden, and activates the cGAS-STING pathway, fostering a pro-inflammatory environment conducive to immunotherapy responsiveness. This dual role, detailed in a June 2025 Oncotarget review, positions CHEK2 as a promising biomarker and therapeutic target to enhance immune checkpoint inhibitor efficacy across diverse malignancies.