The IFN-α used in the study was the classical recombinant IFN –a at a schedule of 3 million units × 3 times weekly s.c. It is possible that the IFN-α formulation and e.g. pegylated versus classical recombinant may and dosage of IFN used may be responsible for the different therapeutic results between the CML IV and the SPIRIT trial. This evidence concerns the gene IFNA1 and chronic myelogenous leukemia, BCR-ABL1 positive.