Differentiation versus cytoreduction during remission induction in acute nonlymphoblastic leukemia treated with sequential high-dose ara-C and asparaginase.

Patients with acute nonlymphoblastic leukemia (ANLL) treated with sequential high-dose ara-C and asparaginase (HiDAC----ASNase) have occasionally exhibited an unusual morphologic picture during induction therapy with a transition period in which large numbers of blasts coexist with returning mature hemopoietic elements. In 2 of 11 adult patients with ANLL treated during a 6-month period using a new protocol of HiDAC----ASNase, the hypoplastic phase typically seen after intense induction never developed. Serial marrow examinations performed 7 to 35 days after treatment showed equal admixtures of blasts and mature elements. Despite these findings, both patients subsequently entered complete remission with morphologically normal bone marrow examinations. The possibility for diagnostic error in interpreting these transition marrows as failed inductions is great and could lead to cessation of supportive therapy or to an unnecessary further course of cytotoxic therapy. This phenomenon raises the biological question, does remission represent leukemia killed or leukemia matured?