New leukemia in the course of therapy of acute lymphoblastic leukemia

We have recently observed the development of second leukemia of a morphologically different type in three patients with acute lymphoblastic leukemia (ALL) while on therapy. The "second" leukemia occurred while on therapy at 23, 27, and 32 months of initial remission. All three were receiving systemic chemotherapy (CT) and prophylactic fractional irradiation to the central nervous system (CNS). The second leukemias in these three cases were one case of juvenile chronic myelogenous leukemia (JCML) and two cases of acute leukemia of the myeloblastic type by the usual morphologic criteria including the presence of Auer rods in one. In two cases a cytogenetically new clone was detected in the remission marrow 10 and 12 months preceding the overt change in clinical status. These three cases demonstrate that second leukemia occurs in patients with ALL and that some late "relapses" fall into this categpry. The possible etiologic role of modern intensive treatment regimens in the development of second leukemia is discussed.