Abstract Background and Objectives In the mammalian cells, there is a relationship between telomere length and both cancer and senescence. Progressive telomere shortening has a role in genomic instability and has been reported in a wide range of human cancers as well as in transformation and progression to hematologic malignancies. Chronic myelogenous leukemia (CML) has different stages in the process of its progression. In this study, we examined the telomere length changes in peripheral blood leukocytes of CML patients in chronic (CP) and blastic phases (BP). Materials and Methods In this descriptive study, we examined the telomere length in 21 CML patients (14 in chronic and 7 in blastic phases) having reffered to Hematology–Oncology and BMT Research Center of Shariati Hospital since March 2004 using Southern blot analysis the results were then compared with age-adjusted normal controls. Data were analyzed through logestic regression and Anova. Results At the time of diagnosis, 71.43% of chronic phase patients had a shortened TRF compared to normal age-adjusted individuals. The mean telomere length values in chronic and blastic phases were 6.98±1.26 kb and 4.81±1.06 kb, respectively it showed significant telomere length reduction in age-adjusted normal controls. Moreover, the mean telomere length values in BP-CML showed significant statistical differences as compared to CP-CML. Mean values of telomere length reduction in CP-CML and BP-CML as compared with normal age-adjusted control group were 3.31±1.38 kb and 5.27±0.9 kb, respectively. Conclusions The significant statistical differences in mean telomere length of CP-CML and BP-CML as compared with age-adjusted normal controls and the apparent differences of TRF in chronic and blastic phases can be useful in prediction of phase of disease progression. � Key words : Chronic myelogenous leukemia, Telomere, Southern blot |