PTCH1 is a reliable marker for predicting imatinib response in chronic myeloid leukemia patients in chronic phase

Patched homolog 1 gene (PTCH1) expression and the ratio of PTCH1 to Smoothened (SMO) expression have been proposed as prognostic markers of the response of chronic myeloid leukemia (CML) patients to imatinib. We compared these measurements in a realistic cohort of 101 patients with CML in chronic phase (CP) using a simplified qPCR method, and confirmed the prognostic power of each in a competing risk analysis. Gene expression levels were measured in peripheral blood samples at diagnosis. The PTCH1/SMO ratio did not improve PTCH1 prognostic power (area under the receiver operating characteristic curve 0.71 vs. 0.72). In order to reduce the number of genes to be analyzed, PTCH1 was the selected measurement. High and low PTCH1 expression groups had significantly different cumulative incidences of imatinib failure (IF), which was defined as discontinuation of imatinib due to lack of efficacy (5% vs. 25% at 4 years, P = 0.013), probabilities of achieving a major molecular response (81% vs. 53% at first year, P = 0.02), and proportions of early molecular failure (14% vs. 43%, P = 0.015). Every progression to an advanced phase (n = 3) and CML-related death (n = 2) occurred in the low PTCH1 group (P<0.001 for both comparisons). PTCH1 was an independent prognostic factor for the prediction of IF. We also validated previously published thresholds for PTCH1 expression. Therefore, we confirmed that PTCH1 expression can predict the imatinib response in CML patients in CP by applying a more rigorous statistical analysis. Thus, PTCH1 expression is a promising molecular marker for predicting the imatinib response in CML patients in CP.