Recent advances in cancer immunotherapy have generated excitement across all fields of oncology. However, the field is still experiencing a lack of predictive biomarkers and patient selection remains difficult. Challenges in discovering predictive biomarkers for cancer immunotherapy involve multiple cell types, multiple mechanisms of T-cell regulation, genetic heterogeneity of tumors, immune components, etc. Cambridge Healthtech Institute’s 3rd Annual Immuno-Oncology Biomarkers and Companion Dx conference program is designed to bring together clinical immuno-oncologists, researchers from pharmaceutical companies and laboratory medicine leaders to discuss the underlying mechanisms of cancer immunotherapy, its predictive biomarkers, as well as existing and emerging clinical assays aimed at improving patient outcomes.