lt; 0.001). Parallel analysis of tumor DNA in both cell-free and cellular DNA from CSF makes the probability of primary or secondary CNS malignancy detection even higher. Conclusions Our prospective, tissue-agnostic approach highlights the feasibility of ctDNA sequencing by a commonplace and affordable method, offering higher sensitivity to detect CNS infiltration with lymphoma than standard cell-analyzing techniques. We accentuate the benefit of a multi-target NGS approach and adequate CSF sampling to obtain satisfactory diagnostic yield. Less invasive liquid biopsy testing by comprehensive NGS complements standard procedures in the diagnostics and management of CNSL patients, especially when encountering limitations.