Clonal stability of initial leukemia in a child with central nervous system relapse 7.4 years after bone marrow relapse of common acute lymphoblastic leukemic.

Second central nervous system (CNS) relapses represent about 7.3% of subsequent recurrences of childhood acute lymphoblastic leukemia (ALL). In most children these subsequent CNS relapses occur during the first 18 months after diagnosis of the first relapse (mean 1.42 +/- 0.73 years). We present a patient who suffered a second ALL relapse in the CNS more than seven years after diagnosis of his first relapse. The leukemic clone was completely stable over more than ten years as shown by minimal residual disease techniques. Possible reasons for the recurrence of the leukemic clone after this very long period of dormancy (e.g. role of the disease site, immune system dysfunction) are discussed.