The immune response is a dynamic reaction of a body, allowing to fight against tumor cells. However, an unbalanced host immune response is highlighted in tumor disease. Abnormal responses lead to autoimmune diseases, whereas low responses favor opportunistic infections and host with tumor cells. The conflicting situations make it difficult to arrange an appropriate immunoassay for immunotherapy. Before human genomics decode in 2004, testing the immune response with this profile of patients remains a challenge. This is due to individual variability so that it impedes immunoassay for personalized immunotherapy. After the fifteen years’ effort, immunoassays are committed to personalized immunotherapy of tumor diseases for precise prediction/prevention, immune targeting therapy, and personalized immunotherapy. Now, identifying new targets at the protein level, SNP at the DNA level, and mRNA expression at the RNA level may guide a new generation of immunoassay. The techniques to test the immune responses to tumor diseases are currently being studied, but they still have many influence factors such as technical standardization and technique selection, and interpretation, and therefore, the chapter gives a comprehensive insight into the immunoassay for personalized immunotherapy.