T lymphoblastic leukaemia and the central nervous system

Of 100 children and adolescents with lymphoblastic leukaemia (ALL) seen over a 6-year period, 25 developed clinically evident infiltration of the central nervous system (CNS), despite early treatment with cranial radiotherapy and intrathecal methotrexate. Nine of these 25 had the features of T ALL, though there were only 17 such patients overall. Not only did those with T ALL get CNS disease more frequently, but they did so much sooner after diagnosis (P less than 0.001) and more commonly had associated facial palsies (P less than 0.05). The tendency to develop CNS infiltration appeared to be significantly related to the possession of T-cell markers (P less than 0.02), but not to the diagnostic white cell count (P = 0.37). These findings suggest that current CNS prophylactic therapy is ineffective in most patients with T ALL.