Comparison of clinical efficacy and toxicity of conventional and optimum biological response modifying doses of interferon alpha-2C in the treatment of hairy cell leukemia: a retrospective analysis of 39 patients.

Hairy cell leukemia (HCL) has been shown to be extraordinarily sensitive to treatment with alpha-interferon (IFN). In order to define clinically effective IFN doses associated with minimal toxicity, the therapeutic efficacy and side effects of recombinant IFN-alpha-2C treatment of HCL were compared for two different dose regimens: 18 patients (group A) received conventional doses of recombinant IFN-alpha-2C (2 x 10(6)U/m2) for a median time of 35 weeks (range 26-52 weeks), and 21 patients (group B) received optimum biological response-modifying doses of IFN-alpha-2C (0.2-0.6 x 10(6)U/m2) for a median time of 31 weeks (range 12-52 weeks). Interferon was administered daily subcutaneously for 3 months and then every second or third day. Induction of neopterin excretion was chosen as the marker for definition of biological response. The smallest IFN dose causing maximum in vivo induction of biosynthesis of the GTP-degradation product neopterin was deemed "biologically optimal." Both dose regimens were effective, but the low-dose regimen was almost free of toxicity. Thus, in HCL patients alpha-IFN related toxicity can be separated from its antineoplastic activity. Low doses of alpha-IFN should be considered for treatment of HCL patients who develop toxic side effects and for primary treatment of HCL patients with severe cytopenia.