Supplementary Material for: Importance of cerebrospinal fluid flow cytometry in pediatric acute lymphoblastic leukemia

Introduction: Acute lymphoblastic leukemia (ALL) is the most common malignancy in children. Central nervous system (CNS) leukemia is usually diagnosed using microscopy and cytospin-based cytology, which has low sensitivity for detecting minimal events. Following the evaluation of bone marrow aspiration samples using flow cytometry (FC), it has been found to be valuable in the risk group stratification and follow-up of ALL. Recently, there have been discussions regarding the routine use of cerebrospinal fluid (CSF) FC analysis for CNS leukemia at diagnosis and/or relapse in ALL protocols. Case presentation: We present a case of ALL in which the CSF cytospin-based cytology analysis revealed no blasts, whereas the FC analysis of the CSF showed 1.6% blasts during the maintenance therapy. The patient developed an overt CNS relapse within three months. Conclusion: We would like to emphasize the importance of using more sensitive techniques to evaluate CNS involvement in patients with ALL.