Central Nervous System Involvement at Diagnosis and Long-Term Outcomes in Paediatric Acute Lymphoblastic Leukemia

Abstract

Central nervous system status at diagnosis is assigned from a single cerebrospinal fluid sample and determines how intensively a child is treated. Two findings unsettle that arrangement: the borderline category carries no consistent prognostic weight, while a bloody tap, which is an event of the procedure rather than of the disease, consistently does. Objectives: To review the published evidence on central nervous system involvement at diagnosis in paediatric acute lymphoblastic leukaemia: how status is classified, what each category predicts, why the studies disagree, what a traumatic tap contributes, and what long-term cost the associated therapy carries.
Material and Methods: Narrative review of cooperative group trial analyses, single-institution protocols, classification algorithms and late-effects studies indexed in PubMed and the major haematology and paediatric oncology journals. Studies were eligible if they reported the prognostic effect of central nervous system status at diagnosis, or the outcomes of central nervous system-directed therapy, in a defined paediatric acute lymphoblastic leukaemia population. No new patient data were generated and no patients were recruited; every estimate quoted is one published by the original investigators. Results: In a cohort of 2,021 children, overt central nervous system disease carried a risk ratio for treatment failure of 2.3 (95% CI 1.4-3.6, p = 0.0005) and traumatic lumbar puncture with blasts a ratio of 1.5 (95% CI 1.02-2.2, p = 0.04), while the borderline CNS2 category was not independently significant. A separate trial found event-free survival of 72.6, 70.3 and 66.7 per cent across CNS1, CNS2 and CNS3 with no significant difference between them, against 58 per cent for traumatic tap with blasts and 82 per cent without (p < 0.01), and identified traumatic tap as an independent factor with a risk ratio of 3.5 (95% CI 1.4-8.8, p = 0.007). A protocol omitting cranial irradiation entirely reported five-year event-free survival of 80.8 per cent with isolated central nervous system relapse in 1.7 per cent and isolated plus combined relapse in 3.0 per cent. Where all patients with any central nervous system finding received intensified intrathecal therapy, status ceased to predict relapse.
Conclusion: The category that predicts most reliably is produced by the diagnostic procedure rather than by the leukaemia, which makes it modifiable in a way the disease is not. Where intensified therapy is given to all patients with any finding, the prognostic effect disappears. Abbreviations: ALL – Acute Lymphoblastic Leukaemia, CNS – Central Nervous System, CSF – Cerebrospinal Fluid, CNSL – Central Nervous System Leukaemia, TLP – Traumatic Lumbar Puncture, LP – Lumbar Puncture, IT – Intrathecal, MTX – Methotrexate, WBC – White Blood Cell, RBC – Red Blood Cell, EFS – Event-Free Survival, RR – Risk Ratio, Gy – Gray.