Isolated bone relapse during hematologic remission in childhood acute lymphoblastic leukemia: report of a metatarsal relapse and review of the literature.

An 11-year-old boy with prior bone marrow and testicular relapses of his acute lymphoblastic leukemia (ALL) developed an isolated metatarsal bone relapse during complete hematologic remission 10 months after completion of chemotherapy. Although there was no radiographic or histologic evidence of additional occult leukemia, the polymerase chain reaction (PCR) technique detected a leukemic clone in both his bone marrow and metatarsal. A literature survey revealed only 10 reported cases of isolated bone relapse occurring during complete bone marrow remission in childhood ALL. Most of these patients had prior bone marrow or extramedullary relapses. The majority experienced subsequent relapses after their isolated bone recurrence. We report a case of isolated bone recurrence, review all previously reported cases, and suggest that PCR elucidation of clonal disease may provide a better understanding of these extremely rare extramedullary events.