Efficacy and toxicity of IFN-α2b combined with cytarabine in chronic myelogenous leukaemia

Newly diagnosed chronic myelogenous leukaemia (CML) patients (n = 65) were treated with interferon (IFN)α2b (5 x 10⁶ IU/d s.c.) combined with monthly courses of cytarabine (20 mg/d s.c. for 14 d). Median age of patients enrolled was 45 years. The endpoints of the study were clinical efficacy and toxicity. The survival rates at 3 years and 5 years were 77% and 56%, respectively. The rate of complete haematological response was 60%. Evaluation of cytogenetic response was available in 29/65 patients. A complete cytogenetic response was seen in 3/29 patients (10%). W.H.O. toxicity grade 3-4 occurred in only 22/523 evaluable treatment cycles. Since the study protocol required intermittent or definitive discontinuation of cytarabine in case of moderate leucopenia (white blood cells (WBC) <5 x 10⁹/l), combined cytopenia (WBC < 5 x 10⁹/l, platelets <100 x 10⁹/l), and isolated moderate thrombocytopenia (<100 x 10⁹/l), the drug had to be discontinued temporarily or definitively in 200 cycles and the dose of cytarabine had to be reduced in 35 cycles. Thus, only 25% of the planned dose of cytarabine could be administered. At this dosage it would appear that cytarabine had no effect on survival and did not improve remission rates. We conclude that a clinical benefit for the addition of cytarabine to the treatment of CML with IFN might only be achieved by the administration of a higher cumulative dose of cytarabine, suggesting that lower leucocyte counts of 2-4 x 10⁹/l have to be tolerated.