Lumbar puncture was performed immediately prior to craniotomy for tumor debulking. After sterile field preparation, the thecal sac was cannulated between the L3 and L5 intervertebral spaces using a 0.61‐mm gauge lumbar puncture needle, and 10 ml of CSF was removed. After collection, CSF, whole blood, and urine samples were immediately placed on ice and then rapidly transferred to a pre‐chilled centrifuge for processing. For urine samples, 0.5 M EDTA was added within an hour of collection. Samples were centrifuged at 1,500 g at 4°C for 10 min. Supernatant was removed and further centrifuged at 20,000 g for 10 min and aliquoted into 2 ml microtubes for storage at −80°C (Sarstedt, Germany). Tumor tissue DNA was extracted and isolated as described previously (Mouliere et al, 2018b (link)). Fluids were extracted using the QIAsymphony platform (Qiagen, Germany). Up to 10 ml of plasma, 10 ml of urine and 8 ml of CSF were used per sample. DNA from cancer plasma, urine, and CSF samples was eluted in 90 μl and further concentrated down to 30 μl using a Speed‐Vac concentrator (Eppendorf, Germany).
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