Perspective on immune oncology with liquid biopsy, peripheral blood mononuclear cells, and microbiome with non-invasive biomarkers in cancer patients.

Antibodies against immune checkpoint inhibitors such as anti-programmed cell death protein 1 (PD-1) and anti-programmed death ligand 1 (PD-L1) play a key role in the treatment of advanced lung cancer. To examine the clinical benefits of these agents, preclinical and clinical studies have been conducted to identify definitive biomarkers associated with cancer status. Analysis of the blood and feces of tumor patients has attracted attention in recent studies attempting to identify non-invasive biomarkers such as cytokines, soluble PD-L1, peripheral blood mononuclear cells, and gut microbiota. These factors are believed to interact with each other to produce synergistic effects and contribute to the formation of the tumor immune microenvironment through the seven steps of the cancer immunity cycle. The immunogram was first introduced as a novel indicator to define the immunity status of cancer patients. In this review, we discuss the progress in the identification of predictive biomarkers as well as future prospects for anti-PD-1/PD-L1 therapy.