Supporting a pathogenetic role for XBP-1s overexpression in the myeloma genesis in this model, several known MM genes that were dysregulated in premalignant Eμ-xbp-1s B cells exhibited similar patterns of alterations in XBP-1s MM cells, including Cyclin D1, MAF, CEBPA, CEBPB, CEBPD, IL6ST (upregulated), and FOS (downregulated). This evidence concerns the gene FOS and plasma cell myeloma.