Deletion of Any of BCR or ABL Gene on Derivative Chromosome 9 Is a Poor Prognostic Marker That Indicates Rapid Disease Progression in Chronic Myelogenous Leukemia

To evaluate the prognostic significance of the submicroscopic deletions of ABL or BCR gene associated with t(9;22) in CML, we investigated the incidence of ABL or BCR deletion on derivative chromosome 9 using fluorescent in situ hybridization (FISH), and analyzed the survival. FISH was performed using LSI BCR/ABL, dual fusion translocation probe on bone marrow cells of 86 patients with CML. Of 86 patients, ABL deletion was detected in 13 (15.1%) patients and BCR deletion in 8 patients (9.3%). Patients with ABL deletion showed shorter event-free survival time (EFS) than those without ABL deletion (P=0.020). Patients with BCR deletion showed significantly short overall survival time (OS) (P=0.039). Patients with ABL and/or BCR deletion (14/86 patients, 16.3%) showed significantly short OS and EFS (median OS: 43.0 months, median EFS: 40.0 months), compared to the patients without any deletions of BCR or ABL gene (median OS: 94.0 months, median EFS: 90.0 months)(P=0.041 for OS, P=0.008 for EFS). Patients with BCR deletion, all except one had a concomitant ABL deletion, suggesting that BCR deletion occurs in conjunction with ABL deletion. In patients with ABL deletion only, BCR/ABL rearrangement with b2a2 mRNA type tended to be more frequent than in patients without any deletion of the two genes (P=0.073). Deletion of any of BCR or ABL gene on derivative chromosome 9 was associated with both short OS and EFS. We conclude that deletion of not only ABL gene, but also BCR gene is a poor prognostic marker that indicates rapid disease progression in CML.