The circadian schedule for childhood acute lymphoblastic leukemia maintenance therapy does not influence event-free survival in the NOPHO ALL92 protocol.

Background: The event-free survival of childhood acute lymphoblastic leukemia (ALL) has been reported to be superior when oral methotrexate (MTX) and 6-mercaptopurine (6MP) maintenance therapy (MT) is administered in the evening compared to the morning.

Procedure: In the ALL92 MT study we prospectively registered the intake of MTX/6MP. The registration was done when blood samples for erythrocyte MTX/6MP metabolite measurements were collected, and referred to the time of intake in the period since last registration.