Recent reports indicate a prognostically detrimental effect of submicroscopic abl-bcr deletions associated with the break and fusion points of the derivative chromosome 9 [der(9)] in chronic myeloid leukemia (CML). In a retrospective cohort of 92 patients with CML, the incidence of an atypical D-FISH pattern, that is consistent with a der(9) deletion was 20%. Complete clinical information was available in 82 patients and revealed no significant differences between 18 deleted and 64 non-deleted cases in platelet count, circulating blast percentage, spleen size, or karyotype profile at presentation. However, der(9)-deleted patients presented with significantly lower hemoglobin levels and higher leukocyte counts. At a median follow-up of 31 months, the incidence of disease transformation, drug therapy response, and survival were similar between the two groups. These results are contrary to previous reports that suggested inferior survival as well as poor response to alpha interferon therapy in CML patients carrying der(9) deletions.
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