Because the estimated yearly costs per patient have been shown to differ [1], we do not dispute the assertions of Messori and colleagues that interferon- treatment may be somewhat more expensive in Germany and Italy than the $1500 figure used as our baseline monthly cost. This uncertainty in cost motivated the sensitivity analysis in our Figure 4. We also agree that $50 000 per QALY seems to be the de facto cutoff for reimbursable therapy.

It seems that the primary reason for this difference in cost of treatment is that our analysis is based on the amount of drug actually delivered rather than the target dose. Because the clinical results achieved are based on the actual dose delivered, this seems a more reasonable basis for estimating treatment costs. The Cancer and Leukemia Group B study [2] found that the average dose delivered was 60%. If the amount of drug delivered in Europe is consistent with this finding, treatment costs would be closer to $1500 per month than $3000 per month. Note also that our model does incorporate an additional cost of $100 per month for administration of interferon- (see page 544 of our article).

In addition, if the promising findings of equal efficacy for lower doses are durable, interferon- might be even more cost-effective than our model suggests. The monthly cost is reported [1] as $496 for a dosage of 2 x 10⁶ U/m² body surface area three times weekly. This results in a marginal cost-effectiveness of less than $5000 per QALY.

Finally, as with any decision analysis, more accurate costs, probabilities, and utilities necessitate sensitivity analyses or reanalyses. In the case of interferon- for chronic myelogenous leukemia in Germany and Italy, we suggest that other sites should consider treatment costs as delivered and then consult our Figure 4 to determine whether interferon- will be cost-effective in their setting.