Detection of occult cerebrospinal fluid involvement during maintenance therapy identifies a group of children with acute lymphoblastic leukemia at high risk for relapse.

We aimed at assessing the clinical significance of the levels of acute lymphoblastic leukemia (ALL) cells in samples of cerebrospinal fluid (CSF) during therapy. We studied 990 CSF samples from 108 patients, at the time of diagnosis (108) and at each time of intrathecal therapy (882). The proportions of leukemic cells in CSF samples were assessed by flow cytometry (FCM).