EUTOS Score Predicts Long-Term Outcome in Chronic Myeloid Leukemia Patients Transitioning from Pre-Imatinib Era to Imatinib upon Availability

Background: The introduction of Tyrosine Kinase Inhibitors (TKI) in the management of Chronic Myeloid Leukemia (CML) has been a paradigm shifting phenomenon, yet the prognosis of CML still relies on pre-TKI era methods. Recently, European Treatment and Outcome Study (EUTOS) for CML has proposed a novel scoring system to prognosticate the outcome of treatment with TKIs that only relies on spleen size and basophil count. Although the validity of the newly proposed score has been tested in various populations worldwide, such a study is yet to be performed in the Indian population. We have looked at all three prognostic scores, namely Sokal score, Hasford/Euro score and EUTOS score, in 377 patients initiated with Hydroxyurea but later transitioned to Imatinib when it was available in India.

Methods: A cohort of 377 patients who were diagnosed as Philadelphia chromosome positive CML over the period of 5 years (Jan, 2003 - Dec, 2008) in Institute of Hematology and Transfusion Medicine, Medical College, Kolkata had been included in the study. All the patients were primarily treated with Hydroxyurea but received Imatinib Mesylate at a later time point. All patients received Hydroxyurea for 6 months or more and received Imatinib for at least 1 year at the time of final follow-up. No patient was treated with second generation tyrosine kinase inhibitors. We divided the patients using all three scores: Sokal, Hasford and EUTOS. The prognostic power of each of the scores were tested based on Overall Survival (OS) and Event Free Survival (EFS). Survival probabilities were estimated by the Kaplan-Meier method and compared by pair-wise log rank, Breslow (Generalized Wilcoxon) test and Tarone-Ware test. The pair-wise method was applied in order to detect distinguishing capacity of each test among different groups.

Results: Only EUTOS score stood out as informative as it was able to distinctly separate high and low risk group patients significantly (p < 0.01). The other two scores, namely Sokal and Hasford could not discriminate between the low and intermediate risk group of patients in terms of OS. When we considered EFS instead of OS for the same analysis, the superiority of EUTOS score over its counterparts again became obvious (p < 0.01).

Conclusion: EUTOS score was able to significantly discriminate between high and low risk patients both in terms of 5 year OS and EFS, while Sokal and Hasford/Euro score failed to discriminate between low and intermediate risk patients. We found EUTOS score to be valid in terms of predicting the outcome of CML patients who transitioned from the pre-imatinib era to Imatinib therapy in our population.