Abstract Immunotherapy response varies widely, making it difficult for physicians to know whether immunotherapy will be effective for a given patient. Indeed, ~80% or more patients with cancer fail to respond to checkpoint inhibitor immunotherapy. In addition to PD-L1 IHC staining, recent studies reported that patients with deleterious mutations in mismatch repair (MMR) genes, high tumor mutation burden (TMB) or microsatellite instability (MSI) are also associated with better clinical response. As tissue biopsy represents a practical challenge due to its insufficient quantity or lack of access, non-invasive molecular has emerged as an efficient complementary test and attracted increasing attention in clinical development of cancer immunotherapy. With Predicine's gene RARDAR technology, we developed a blood-based PrediSeq NGS panel to capture genomic alterations in 180 cancer genes including tumor mutation burden (TMB) and microsatellite instability (MSI) and a Predi-CI (Cancer Immunotherapy) panel to measure dynamic expression change of 212 genes related to immune cells or immune responses. Technical validation was performed to evaluate assay sensitivity, specificity and accuracy using reference samples with known genetic profiling. The panels have been further tested using tissue biopsy and plasma samples from cancer patients. The development of PrediSeq Panel and Predi-CI RNA gene expression tests offer a comprehensive solution to stratify and monitor cancer patients who may benefit from cancer immunotherapy. Citation Format: Feng Xie, Jianjun Yu, Shidong Jia. Detection and validation of cancer immunotherapy biomarkers in blood [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3659.