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Central nervous system relapse surveillance by serial beta 2-microglobulin measurements in childhood acute lymphoblastic leukemia.

Beta 2-microglobulin (beta 2m) is synthesized particularly in lymphocytes. Its value for early detection of central nervous system (CNS) involvement in acute lymphoblastic leukemia in children was tested by serial determinations. Before 9 overt CNS relapses, the mean increase of the cerebrospinal fluid (CSF) beta 2m concentration was 588 micrograms/l/month (range: -50 to +2020), which was significantly higher than the steady levels during maintenance treatment. Although the absolute value of CSF beta 2m was increased to 1 430 micrograms/l in the group with overt CNS relapse, individual variations in CSF beta 2m before a relapse were so great that no difference was seen between samples from CSF with or without lymphoblasts. The ratio between beta 2m in the CSF and in serum did not increase in serial samples prior to overt relapse, but the ratio was higher in patients with CNS relapse compared with a control group on maintenance therapy. In 9 children without CNS leukemia, the beta 2m concentration in CSF and serum decreased to a nadir 4 weeks after the start of induction treatment. The subsequent increase of CSF beta 2m was similar to the increase before a CNS relapse. Mean values of CSF beta 2m changes differed between groups of children with and without CNS leukemia early in the induction phase and during the maintenance treatment, but the wide range in individual values made serial beta 2m determinations unsuitable for detecting a CNS relapse.