CSF miRNA expression classification tree correctly diagnosing 95.7% of patients with PCNSL and 96.7% of control patients. Relative expression cutoff levels of ≥ 8.0 REL for miR-21, ≥ 1.4 REL for miR-19b, and ≥ 2.5 REL for miR-92a, respectively, were applied for diagnostic placements as depicted.