Advances in Immunotherapy for Solid Tumors: A Systematic Literature Review

Abstract

Immunotherapy has revolutionized the management of solid tumors by harnessing the host immune system to recognize and eliminate malignant cells. This systematic review synthesizes current evidence regarding the mechanisms, clinical efficacy, safety profiles, and emerging developments of major immunotherapeutic modalities in solid malignancies. A comprehensive literature search was conducted across multiple electronic databases following PRISMA guidelines, resulting in the inclusion of 156 studies encompassing clinical trials, retrospective cohorts, and systematic reviews. The review evaluates immune checkpoint inhibitors, adoptive cell therapies including chimeric antigen receptor (CAR) T-cell strategies, oncolytic virus therapies, and biomarker-driven precision immunotherapy approaches. Landmark trials such as CheckMate 067, KEYNOTE-024, and JAVELIN Renal 101 demonstrate significant survival benefits in melanoma, non-small cell lung cancer, and renal cell carcinoma, respectively, although efficacy varies substantially across tumor types. Emerging CAR-T therapies and oncolytic viral platforms show promising yet evolving roles in overcoming tumor immune resistance and converting immunologically cold tumors into responsive phenotypes. Additionally, predictive biomarkers including programmed death-ligand 1 expression, tumor mutational burden, microsatellite instability, circulating tumor DNA dynamics, and gut microbiome composition are critically examined for their role in optimizing patient selection and treatment outcomes. Despite remarkable therapeutic advances, challenges such as immune-related toxicities, tumor heterogeneity, resistance mechanisms, and limited efficacy in certain solid tumors persist. Future research directions emphasize rational combination strategies, multi-omics biomarker integration, and innovative cellular engineering approaches to enhance durability, safety, and clinical applicability. Collectively, this review provides a comprehensive and clinically relevant framework for understanding the evolving landscape of immunotherapy in solid tumors.