Accessing the subarachnoid space via intrathecal needle placement can be done in nonhuman primates (NHPs) and other species to collect cerebral spinal fluid (CSF) or to deliver agents into the CSF.

CSF-ctDNA was detected in 59% of cases and showed high concordance (84%) with tumor mutations. Lower variant allelic frequency in CSF-ctDNA was associated with significantly worse survival outcomes.