Prediction of Immune checkpoint inhibitors benefit from routinely measurable peripheral blood parameters

Immunotherapy of cancer has been the most remarkable advance in cancer therapy in the last several years with the successful introduction of monoclonal antibody drugs that block inhibitory immune receptors to invigorate immune attack against tumors. With the introduction of these drugs the parallel need of predictive markers of response has arisen. Beyond markers from the tumor and the tumor micro-environment, the peripheral blood supplies several biomarkers for response that have been reported individually or in combinations to provide valuable predictive information. These include the number of circulating cell subsets, various ratios of them and combinations of factors that also encompass biochemical measurements such as LDH. Peripheral blood biomarkers are usually obtained during the routine patient evaluations, methodology is well-calibrated for the routine practice and their acquisition does not require extra infrastructure or financial resources. This paper will review available data on predictive markers for immune checkpoint inhibitors (ICIs) from peripheral blood, including biomarkers that have been less extensively studied. In addition, it will discuss ways forward for the use of peripheral blood biomarkers in immunotherapy prognostication.