Monitoring checkpoint inhibitors: predictive biomarkers in immunotherapy.

Immunotherapy has become the fourth cancer therapy after surgery, chemotherapy, and radiotherapy. In particular, immune checkpoint inhibitors are proved to be unprecedentedly in increasing the overall survival rates of patients with refractory cancers, such as advanced melanoma, non-small cell lung cancer, and renal cell carcinoma. However, inhibitor therapies are only effective in a small proportion of patients with problems, such as side effects and high costs. Therefore, doctors urgently need reliable predictive biomarkers for checkpoint inhibitor therapies to choose the optimal therapies. Here, we review the biomarkers that can serve as potential predictors of the outcomes of immune checkpoint inhibitor treatment, including tumor-specific profiles and tumor microenvironment evaluation and other factors.