Relation between cereblon expression and survival in patients with newly diagnosed multiple myeloma treated with thalidomide

Introduction: Cereblon (CRBN) expression has been described to be essential for the activity of Thalidomide and Lenalidomide. This suggests that presence and possibly increased level of CRBN expression would be associated with better outcome in Thalidomide/Lenalidomide treated patients. The aim of this study was to evaluate CRBN expression in relation to outcome in patients receiving Thalidomide maintenance. Patients and methods: The HOVON-65/GMMG-HD4 trial is a multi-center, phase III trial, comparing Bortezomib in induction and post-intensification vs. conventional chemotherapy and daily Thalidomide 50 mg for 2 years post-intensification in newly diagnosed MM patients. This trial demonstrated that Bortezomib during induction and maintenance improved CR and achieved superior PFS and OS (Sonneveld et al., JCO, July 16, 2012). Gene expression profiling was performed at the start of the trial by Affymetrix U133 Plus 2.0 GeneChip, and was available for 96 patients which started Thalidomide maintenance. CRBN expression levels were based on a combined value of probe sets 218142-s-at and 222533-at. CRBN expression was validated using real-time PCR. All survival analyses were performed in SPSS, with survival time taken from the start of maintenance. Results: In patients receiving Thalidomide maintenance, increased CRBN expression was significantly associated with longer progression free survival (p=0.005, hazard ratio = 0.7) and longer overall survival (p=0.04, hazard ratio= 0.7). Using Kaplan-Meier analysis for visualization and using the median expression to define high and low expression, a significant separation was found for PFS (Log rank p=0.009) but not for OS (Log rank p=0.13). No association was observed between CRBN expression and PFS/OS after Bortezomib maintenance (PFS, p=0.4, hazard ratio=1.1; OS, p=0.7, hazard ratio=1.1). Multivariate Cox regression analysis was performed using the covariates ISS, CRBN and high-risk cytogenetics, defined as having del(17p) and/or 1q gain and/or t(4;14). Higher CRBN levels remained significantly related to longer PFS (hazard ratio 0.7, p=0.03), but not OS (hazard ratio of 0.8, p=0.3). High-risk cytogenetics and ISS were both significant in both PFS and OS multivariate models, with hazard ratios of 2.8 and 3.6, for high-risk cytogenetics and 2.5 and 5.5, for ISS stage 3, respectively (p=0.0004, p=0.003, high-risk cytogenetics and p=0.01 and p=0.005, ISS stage 3, respectively). Conclusion: These data suggest use of CRBN as a biomarker for thalidomide outcome, but further analysis in other Thalidomide trials is required to validate this finding