Mercaptopurine is used as maintenance therapy for acute lymphoblastic leukemia. During which phase of ALL therapy is this agent typically used?

• A. Induction phase
• B. Maintenance phase
• C. Consolidation phase
• D. Relapse therapy

Answer: (B)

The main idea is that maintenance therapy in ALL is meant to sustain remission after the disease has been brought under control, rather than to crash the disease quickly. Mercaptopurine is a purine analogue that interferes with DNA and RNA synthesis, which slows the renewal of leukemic cells. Because this phase aims for long-term suppression with a low-intensity, ongoing approach, mercaptopurine is given over an extended period after induction and consolidation have achieved remission. It’s not the rapid, high-intensity treatment used to induce remission, nor the intensified course used to eradicate residual disease during consolidation, and it isn’t planned as relapse therapy. By continuing mercaptopurine during maintenance, the risk of relapse is reduced while keeping toxicity manageable. Monitoring and dose adjustments (for example based on blood counts and TPMT-related considerations) help balance efficacy and safety throughout this extended phase.