Very late recurrence of childhood acute lymphoblastic leukemia treated with chemoimmunotherapy: a report of three cases occurring 19, 11, and 9 years after discontinuation of chemotherapy

Current therapeutic modalities for childhood acute lymphoblastic leukemia (ALL) are associated with a high cure rate, and recurrences more than 4 years after therapy cessation are very unusual. We report three cases of exceptionally late recurrences of childhood ALL after cessation of chemotherapy (CT) given for respective periods of 8, 7, and 24 months. CT was followed by maintenance immunotherapy (IMT) with Bacillus Calmette-Guérin (BCG) and allogeneic leukemic lymphoblasts pretreated with formaldehyde or irradiated in vitro. Leukemic recurrences were observed 19, 11, and 9 years after cessation of CT and appeared morphologically similar to the original blasts. A second complete remission was easily achieved in all three patients, but two went on to repeated relapse (one has died following the fourth recurrence). We speculate that some residual leukemic cells, remaining after the inadequate, short-term CT, were responsible for these unusual evolutions, and we question a possible delaying role of IMT in prolonging remission. Other possible etiologies are discussed.