This gene expression set contains data from patients included in the HOVON131 clinical trial. Using this data the relation between circulating tumor cells and gene expression patterns was studied in newly diagnosed multiple myeloma patients. Circulating tumor cells are a known prognostic factor in multiple myeloma. However, the causes of high circulating tumor cells have been insufficiently characterised. This study aimed to identify factors involved in high circulating tumor cell count, using a model to correct for important contributing factors to this phenotype, which is closely associated with aggressive disease. Overall design: 109 samples were analysed, which were taken from 109 individual patients. Samples were derived from bone marrow aspirates, which were subjected to enrichment of MM cells using CD138 specific beads. RNA sample workup was performed according to the instructions for use of the MMprofilers at the SkylineDx reference lab (SkylineDx, Rotterdam, The Netherlands). Samples were hybridized to Affymetrix HG-U133 plus2 chips, using Affymetrix Inc. (Santa Clara, CA) 3' IVT PLUS reagents. All samples passed wet lab and data QC acceptance criteria. Gene expressions were MAS5.0 normalized (values below 30 were truncated) with a target value of 1500. The MMprofiler CE IVD assay was used to obtain SKY92 scores, classifying a patient as high risk or standard risk.