Treatment of acute lymphoblastic leukaemia: effect of variation in length of treatment on duration of remission. Report to the Medical Research Council by the Working Party on Leukaemia in Childhood.

Patients with acute lymphoblastic leukaemia (ALL) were allocated at random either to stop maintenance chemotherapy after six 12-week courses or continue with a further six. The main difference between the two groups was in the incidence of bone-marrow relapse within nine months after stopping treatment. Such relapses occurred less in older patients and those with higher leucocyte counts initially than in those who appeared to have the best prognosis--namely, those with typical low-count childhood ALL. No patient given prophylactic irradiation to cranium and spine combined with intrathecal methotrexate suffered meningeal relapses, whereas among those not given such prophylaxis the lack of benefit from continuing treatment was mainly attributable to meningeal relapses.