e13604 Background: Glioblastoma is the most common and aggressive brain tumor, with a high recurrence rate and low survival. We are increasing our understanding of its biology, and more targeted therapeutical agents are available. However, the GBM prognosis has not improved over the last decades. Multiple clinical trials on Cell and Gene Therapies are ongoing but, there is a huge need to define standardized and innovative strategies to promote better patient selection, implement adaptative designs and specific laboratory assays, and tailor the clinical endpoint assessments. Methods: Medical experts panel agreed on the following insights and gave advice to improve the design and conduct of GBM trials. Results: The criteria for selecting patients are not uniform among studies. The 2021 WHO Classification of central nervous system tumors has yet to be universally adopted, and different tumor entities are being treated as GBM according to the prior 2016 classification. Furthermore, the required genetic testing panel is only available in some countries as part of routine testing. A wide range of CGT therapies are being studied with different mechanisms of action and are well suited to be administered as combinatory regimens and multiple-dosing schedules to boost the antitumor effect. The implementation of master protocols offers the possibility to test different schedules to identify the most promising for further investigation during early phase development. There is a lack of biomarkers for the patient- or cancer-specific sensitivity and the efficacy of CGT. This is important not only to target clinical treatments to the appropriate patients and identify responding/non-responding patients early during treatment but also to improve the preclinical models and identify targets for further therapeutic development. Investigators should use standard endpoint criteria when reporting clinical outcomes. It has been common to refrain from introducing any preliminary-effect objective in the early stages. This tendency changes after guidance from experts and regulatory agencies about maximizing early-phase data. Another vital endpoint in the early phases is assessing patient immunogenicity against CG therapy based on humoral and cell virus-specific and tumor-specific immune responses. This is especially important as there are significant concerns in translating preclinical safety results to the clinic due to the species-specificity of different viruses and critical differences between immune systems. Conclusions: Today, the purpose of treatment for GBM is to extend the survival period and to manage the disease while preserving the patient’s quality of life. The goal of CGT is a durable complete response, but to achieve this target, we will need a deep analysis of how we perform clinical trials and move to an expert and tailored research environment.