Simple SummaryThere is still a lack of reliable molecular predictors to achieve major molecular response (MMR,BCR::ABL1≤ 0.1% IS) within the first year of treatment with tyrosine kinase inhibitors (TKI) in the therapeutic management of newly diagnosed chronic myeloid leukemia (CML). Employing a proprietary fluorogenic flow cytometry assay, we recently identified separase proteolytic activity as a potential marker of molecular response andBCR::ABL1positivity of CD34+ cells in TKI-treated CML patients. Here, we analyzed the expression and predictive value ofESPL1/Separase,PTTG1/Securin andPTTG1IP/Securin interacting protein transcript levels in white blood cells of CML patients (n= 97) at the time of diagnosis by means of qRT-PCR. We establish a novel distance (cut-off) score based onESPL1,PTTG1andPTTG1IPgene expression levels that can serve as predictors of TKI non-response in about 10% of analyzed non-responding patients and may have potential benefit for the risk stratification of CML patients.AbstractThe achievement of major molecular response (MMR,BCR::ABL1≤ 0.1% IS) within the first year of treatment with tyrosine kinase inhibitors (TKI) is a milestone in the therapeutic management of patients with newly diagnosed chronic myeloid leukemia (CML). We analyzed the predictive value of gene expression levels ofESPL1/Separase,PTTG1/Securin andPTTG1IP/Securin interacting protein for MMR achievement within 12 months. Relative expression levels (normalized toGUSB) ofESPL1,PTTG1andPTTG1IPin white blood cells of patients (respondersn= 46, non-respondersn= 51) at the time of diagnosis were comparatively analyzed by qRT-PCR. 3D scatter plot analysis combined with a distance analysis performed with respect to a commonly calculated centroid center resulted in a trend to larger distances for non-responders compared to the responder cohort (p =0.0187). Logistic regression and analysis of maximum likelihood estimates revealed a positive correlation of distance (cut-off) with non-achieving MMR within 12 months (p =0.0388, odds ratio 1.479, 95%CI: 1.020 to 2.143). Thus, 10% of the tested non-responders (cut-off ≥ 5.9) could have been predicted already at the time of diagnosis. Future scoring ofESPL1,PTTG1andPTTG1IPtranscript levels may be a helpful tool in risk stratification of CML patients before initiation of TKI first = line treatment.