Isolated extramedullary relapse in childhood acute lymphocytic leukemia

Although the vast majority of children with acute lymphocytic leukemia attain remission with modern therapies, an unacceptably high number will suffer a disease relapse. Both the duration of remission and the site of relapse are important prognostic factors. This review focuses on leukemic relapse isolated to sites outside the bone marrow (extramedullary sites). Data from cooperative study groups as well as large single institutions are reviewed with respect to the incidence of isolated extramedullary relapse as well as the outcome following relapse. The unique anatomic and physiologic properties of the testes and the central nervous system-the two most common sites of isolated extramedullary relapse-are discussed. Finally, the evolution of leukemia therapy is reviewed, bringing into focus the goals and challenges of future therapeutic endeavors.