Advancing Cancer Treatment: A Review of Immune Checkpoint Inhibitors and Combination Strategies.

Simple Summary: Cancer treatment has advanced greatly over the past decades of experiments and trials with immune checkpoint inhibitors, which help the immune system recognize and attack cancer cells. Chemotherapy is a standard and common treatment for cancer; however, it can also damage healthy cells. Immunotherapy has shown promising efficacy in lung, liver, melanoma, and triple-negative breast cancers (TNBCs). However, its effectiveness is limited because some patients are resistant to this treatment. This review explores the latest combination strategies to enhance the response to treatment, including radiotherapy, metabolic reprogramming, microbiome modulation, and dual checkpoint blockade. In addition, biomarkers and novel immune checkpoints are being explored to optimize patient outcomes. This review aims to improve ICI-based therapies and guide future cancer research by identifying effective combination approaches and understanding resistance mechanisms. The findings are not only essential for clinicians to develop more personalized cancer treatments but also to offer new hope to patients with hard-to-treat cancers. BACKGROUND: Immune checkpoint inhibitors (ICIs) have considerably revolutionized cancer treatment by enhancing the immune system's ability to recognize and attack tumor cells, unlike conventional therapies. ICIs have demonstrated significant efficacy in non-small cell lung cancer (NSCLC), hepatocellular carcinoma (HCC), melanoma, and triple-negative breast cancer (TNBC) by targeting checkpoint proteins such as PD-1, PD-L1, and CTLA-4. However, challenges, side effects, and limited response rates necessitate the use of combination strategies to optimize therapeutic outcomes. METHODS: This review pooled evidence to enhance ICI efficacy, focusing on tumor microenvironment (TME) modulation, metabolic reprogramming, microbiome-based interventions, radiotherapy, and novel immune checkpoints. A literature search through published journals and real-world data provided the relevant information. The studies included findings on combination therapy approaches for NSCLC, HCC, melanoma, and TNBC. Data on progression-free survival (PFS), overall survival (OS), and response rates were compiled into tables. RESULTS: Combination strategies significantly improved ICI responses compared to traditional therapies; for example, radiotherapy enhanced tumor antigen presentation, and JAK inhibitors and metabolic regulators restored immune sensitivity. Microbiome modulation influences the immune response by targeting gut bacteria. Tyrosine kinase inhibitors (TKIs) combined with ICIs have enhanced PFS and OS, and novel immune checkpoints such as LAG-3, TIM-3, and TIGIT have shown efficacy in overcoming resistance. Furthermore, predictive biomarkers can be used to optimize treatment. CONCLUSIONS: ICI remains a cornerstone of cancer immunotherapy, but its full potential relies on combination strategies and biomarker-driven approaches for patients who may not experience a favorable response to ICI therapy. Future research should focus on personalized ICI therapies to improve the response in various cancers, resulting in more effective cancer immunotherapy.