A 6-year-old girl with newly diagnosed common ALL is planned for multiagent induction chemotherapy. Why must additional central nervous system-directed therapy be given even when the initial CSF examination shows no blasts?

• A Chemotherapeutic agents used in induction cross the blood-brain barrier poorly
• B Intrathecal therapy prevents transformation to AML
• C CSF cytospin fails to detect blasts in over half of children at diagnosis
• D The CNS acts as a pharmacologic sanctuary site where leukemic cells survive systemic chemotherapy ✓

Explanation

The CNS is a sanctuary site: many systemic agents penetrate the blood-brain and blood-CSF barriers poorly, so occult leukemic blasts sheltering there can survive induction and later seed relapse. Routine CNS-directed prophylaxis, using intrathecal methotrexate with or without systemic agents and cranial radiotherapy in selected high-risk cases, reduced CNS relapse dramatically and is credited as a major reason for the high cure rates in childhood ALL.

Reference: Nelson Textbook of Pediatrics, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.