Background :The complementary ABL-BCR gene rearrangement is formed at chromosome 9 parallel to the Ph chromosome at der(22)t(9;22), which has been found deleted in a minority of chronic myelogenous leukemia (CML) patients. This study was designed to analyze the deletion status of ABL and/or BCR on derivative chromosome 9 and to evaluate the prognostic significance of the deletion of these genes in CML. Method :We studied 79 patients who were diagnosed as CML at Seoul National University Hospital between January 1997 and February 2002. The deletion status of ABL and BCR on derivative chromosome 9 was investigated by interphase fluorescent in situ hybridization (FISH) method. Result :ABL deletion was detected in 14 (17.7%) patients and BCR deletion was observed in 8 patients (10.1%). Event-free survival time of the patients with ABL and/or BCR deletion (19.0%) was shorter than that of the patients without any deletion of these two genes (median, 40.0 months vs. 92.0 months)(P=0.027). Twenty seven patients progressed to blast crisis in this period. The period to blast crisis was also shorter in 8 patients with ABL and/or BCR deletion than in 19 patients without any gene deletion (P=0.044). The b2a2 mRNA type was more frequent in the patients with ABL deletion only than in the patients without any gene deletion (P=0.034). Conclusion :Event-free survival time and the period to blast crisis were significantly shorter in patients with deletion of ABL and/or BCR on derivative chromosome 9. ABL and/or BCR deletion can be a significant prognostic marker that indicates rapid disease progression.

Keywords: Chronic myelogenous leukemia, CML, Philadelphia chromosome, Fluorescence in situ hybridization, FISH, ABL deletion, BCR deletion, derivative chromosome 9