Definitions

Although the terms "primary induction failure," "relapsed," and "refractory" are often used, consistent definitions are lacking. "Primary induction failure" is generally used to describe those patients who fail to respond to an initial induction attempt. What constitutes an "induction attempt" is less certain. If induction is taken to mean a single cycle of standard-dose cytarabine plus daunomycin, at least 40% of failing patients will achieve a complete remission (CR) with a second cycle of treatment.12 Although failure to achieve a CR with one cycle of therapy ultimately indicates a poor prognosis, because almost half of patients who fail a single cycle will still achieve a CR with a second cycle of the same therapy, the term primary induction failure should be reserved for patients who fail two cycles of standard-dose therapy. Less is known about patients who fail a single-induction cycle containing high-dose cytarabine. The term "refractory AML" has been used to describe a subset of relapsed AML that is unlikely to respond to further salvage chemotherapy. Hiddemann et al. were among the first to provide a system of definitions and, based on a study of 180 patients, defined "refractory" as patients who had failed initial induction therapy, those who relapsed within 6-12 months of first CR, and those in second or subsequent relapse.3 Estey et al. performed a retrospective study of 206 patients treated with chemotherapy for recurrent AML at the MD Anderson Cancer Center and were able to identify four groups, based principally on the duration of first CR.4 Patients with an initial CR in excess of 2 years had a 73% likelihood of obtaining a second CR. Those with an initial CR duration of 1-2 years had a 47% CR rate. Patients with an initial CR lasting less than 1 year or with no initial CR receiving their first salvage attempt had a subsequent

Table 9.1 Categories of previously treated active leukemia

Category Comment

Primary induction failure Following two cycles of conven tional dose therapy

Table 9.1 Categories of previously treated active leukemia

Category Comment

Primary induction failure Following two cycles of conven tional dose therapy

Refractory

First relapse after initial remission

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