GEN-7 Liquid biopsy in brain tumor patients -The present and future-

We have previously published liquid biopsy for the diagnosis of brain tumors including PCNSL (JCO Precision Oncology, 2019; Leukemia and Lymphoma, 2019) and diffuse midline gliomas (DMG) (Diagnostics, 2021). We used the Maxwell RSC cfDNA extraction kit to extract circulating tumor DNA (ctDNA from) 1 milliliter of cerebrospinal fluid (CSF), and droplet digital PCR to detect MYD88 L265P mutations in PCNSL and H3F3A K27M mutations in DMG. From our initial experience, we were able to detect a high rate of MYD88 mutations in PCNSL, but not H3F3A mutations in DMG. We also observed that higher concentrations of ctDNA were obtained when prompt centrifugation and storage were done after obtaining CSF. Application of liquid biopsy to early detection of relapse and monitoring of treatment relapse are highly anticipated. In cases of PCNSL, we perform liquid biopsy when relapse is suspected on post-contrast MRI. However interestingly, the rate of MYD88 mutations detected is lower than that of newly-diagnosed cases. We would also like to share our experience performing liquid biopsy in conjunction with CSF cytology in brain tumor patients with evidence of leptomeningeal disease. From our initial experience, we would like to discuss the present limitations and future prospects of liquid biopsy in brain tumor patients.