Fusion between M-bcr and abl results in the 'small' abl/bcr fusion gene encoding a 'small' ABL/BCR transcript, detectable in 65% patients suffering from CML [6], which is translated into an ABL/BCR protein with a theoretical molecular mass of about 40 kDa – p40(ABL/BCR) (Zheng et al. in preparation). This evidence concerns the gene BCR and chronic myelogenous leukemia, BCR-ABL1 positive.