In which of the following types of leukemia is methotrexate administered for CNS prophylasxis:

Answer is A (ALL) Preventive treatment or CNS prophylaxis against the possibility of later central nervous system involvement is routinely administered in both children and adults with Acute Lymphoblastic Leukemia (ALL). The concept of CNS prophylaxis in ALL is based on the fact that most children with ALL have subclinical CNS involvement at the time of diagnosis. The meninges harbour occult leukemic cells and act as a sanctuary site where leukemia cells are protected from systemic chemotherapy because of blood brain barrier. Note: CNS Relapse is very uncommon in AML.