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The current standard of diagnosing central nervous system (CNS) lymphoma is stereotactic biopsy, however the procedure has a risk of surgical complication. Liquid biopsy of the CSF is a less invasive, non‐surgical method that can be used for diagnosing CNS lymphoma. In this study, we established a clinically applicable protocol for determining mutations in MYD88 in the CSF of patients with CNS lymphoma. CSF was collected prior to the start of chemotherapy from 42 patients with CNS lymphoma and matched tumor specimens. Mutations in MYD88 in 33 tumor samples were identified using pyrosequencing. Using 10 ng each of cellular DNA and cell‐free DNA (cfDNA) extracted from the CSF, the MYD88 L265P mutation was detected using digital PCR. The conditions to judge mutation were rigorously determined. The median Target/Total value of cases with MYD88 mutations in the tumors was 5.1% in cellular DNA and 22.0% in cfDNA. The criteria to judge mutation were then determined, with a Target/Total value of 0.25% as the cutoff. When MYD88 mutations were determined based on these criteria, the sensitivity and specificity were 92.2% and 100%, respectively, with cellular DNA; and the sensitivity and specificity were 100% with cfDNA. Therefore, the DNA yield, mutated allele fraction, and accuracy were significantly higher in cfDNA compared with that in cellular DNA. Taken together, this study highlights the importance of detecting the MYD88 L265P mutation in cfDNA of the CSF for diagnosing CNS lymphoma using digital PCR, a highly accurate and clinically applicable method., Development of a liquid biopsy for less invasive diagnosis of CNS lymphoma is in progress. In this study, the conditions for detecting the MYD88 L265P mutation by digital PCR were set, and extremely high accuracy was confirmed. This method is fully clinically feasible.

background: IDH mutant astrocytoma has good prognosis compared with IDH wildtype one. In IDH mutant astrocytoma, However, patients with CDKN2A/B homozygous deletion (HD) are worse prognosis than non CDKN2A/B HD. Here we analyzed the prognosis of glioma patients identified with CDKN2A/B HD in our hospital. method: There were 62 cases, and female was 26. Mean age of all cases was 41.2 and median age was 38. In IDH gene status, R132H was 59 cases (95.2%), R172K 2 (3.2%) and R132S 1 (1.6%). All 62 cases were TERT wildtype. CDKN2A/B HD were 12 cases (19.4%). In log-rank test, the group of CDKN2A/B HD was poor prognosis than non HD. In astrocytoma grade 3, CDKN2A/B HD had significantly poor prognosis (p=0.002). In Cox proportional hazard model analysis, CDKN2A/B HD was effective predictive prognostic factor as well as age and grading (p=0.03). discussion/conclusion: We showed that CDKN2A/B HD was good predictive prognostic factor in IDH mutant astrocytoma.