Childhood Acute Lymphoblastic Leukemia Treatment (PDQ®): Treatment - Health Professional Information [NCI] - Postinduction Treatment for Childhood ALL
Backbone of maintenance therapy
The backbone of maintenance therapy in most protocols includes daily oral mercaptopurine and weekly oral or parenteral methotrexate. Clinical trials generally call for the administration of oral mercaptopurine in the evening, which is supported by evidence that this practice may improve EFS. On many protocols, intrathecal chemotherapy for CNS sanctuary therapy is continued during maintenance therapy. It is imperative to carefully monitor children on maintenance therapy for both drug-related toxicity and for compliance with the oral chemotherapy agents used during maintenance therapy. Nonadherence to treatment with 6-mercaptopurine (6-MP) in the maintenance phase is associated with a significant increase in the risk of relapse.
Treating physicians must also recognize that some patients may develop severe hematopoietic toxicity when receiving conventional dosages of mercaptopurine because of an inherited deficiency (homozygous mutant) of thiopurine S-methyltransferase, an enzyme that inactivates mercaptopurine.[33,34] These patients are able to tolerate mercaptopurine only if dosages much lower than those conventionally used are administered.[33,34] Patients who are heterozygous for this mutant enzyme gene generally tolerate mercaptopurine without serious toxicity, but they do require more frequent dose reductions for hematopoietic toxicity than do patients who are homozygous for the normal allele.
Evidence (maintenance therapy):
- In a meta-analysis of randomized trials comparing thiopurines, 6-thioguanine (6-TG) did not improve the overall EFS, although particular subgroups may benefit from its use. The use of continuous 6-TG instead of 6-MP during the maintenance phase is associated with an increased risk of hepatic complications, including veno-occlusive disease and portal hypertension.[36,37,38,39,40] Because of the increased toxicity of 6-TG, 6-MP remains the standard drug of choice.
Pulses of vincristine and corticosteroid are often added to the standard maintenance backbone, although the benefit of these pulses within the context of intensive, multiagent regimens remains controversial.
Evidence (vincristine/corticosteroid pulses):
- A CCG randomized trial conducted in the 1980s demonstrated improved outcome in patients receiving monthly vincristine/prednisone pulses. A meta-analysis combining data from six clinical trials from the same treatment era showed an EFS advantage for vincristine/prednisone pulses.[42,43]
- A systematic review of the impact of vincristine plus steroid pulses from more recent clinical trials raised the question of whether such pulses are of value in current ALL treatment, which includes more intensive early therapy.
- In a multicenter randomized trial in children with intermediate-risk ALL being treated on a BFM regimen, there was no benefit associated with the addition of six pulses of vincristine/dexamethasone during the continuation phase, although the pulses were administered less frequently than in other trials in which a benefit had been demonstrated.
- A small multicenter trial of average-risk patients demonstrated superior EFS in patients receiving vincristine plus corticosteroid pulses. In this study, there was no difference in outcome based on type of steroid (prednisone vs. dexamethasone).[Level of evidence: 1iiA]