Hematopoietic recovery following induction therapy of acute leukemias: prognostic implications and a new look at the definition of remission.

Adult patients with acute leukemia may expect relatively high initial response rates with chemotherapy, but most will ultimately relapse and die from their disease. Prognostic models based mostly on pretreatment factors have been established and attempt to identify good- and poor-prognosis patients to assign them to risk-adapted therapies. Although achievement of a complete response (CR) is still the most significant clinical endpoint for survival, criteria for CR are arbitrarily defined. Besides the questionable numerical cut-off points that characterize CR, remission is not an all-or-none phenomenon. The shorter the time to CR, the better is the long-term outcome in chemotherapy-treated patients. Response during therapy can thus supplement pretreatment prognostic information. Shorter time to platelet recovery in patients achieving CR has been demonstrated to be associated with longer overall and disease-free survival in patients with acute lymphoblastic leukemia (ALL), including Philadelphia chromosome-positive ALL. Focusing on hematpoietic recovery may reflect a multitude of biological processes that occur during response to therapy and provide important information about the host's ability to fight and contain residual leukemic cells. It may complement current approaches to measuring minimal residual disease by flow cytometry and polymerase chain reaction (PCR).