B2M and central nervous system leukemia: Critically, patients with CNS involvement of hematopoietic malignancies had significantly higher CSF β2-M levels than those without (CNSL vs. NCNSL: 3.0 mg/L vs. 1.2 mg/L; CNS leukemia vs. non-CNS leukemia: 1.6 mg/L vs. 1.1 mg/L; both p < 0.001) (Figs. 2a, b).