Clinical and Biological Implications of MYC Activation: A common difference between MGUS and newly diagnosed multiple myeloma

Events mediating transformation from the pre-malignant monoclonal gammopathy of undetermined significance (MGUS) to multiple myeloma (MM) are unknown. We analyzed a gene expression datasets generated on the Affymetrix U133 platform from 22 MGUS and 101 MM patients using gene-set enrichment analysis. Genes over-expressed in MM were enriched for cell cycle, proliferation and MYC activation gene-sets. Upon dissecting the relationship between MYC and cell cycle genesets, we identified and validated a MYC activation signature dissociated from proliferation. Applying this signature, MYC is activated in 67% of myeloma, but not in MGUS. This was further confirmed by immunohistochemistry using membrane CD138 and nuclear MYC double staining. We also showed that almost all tumors with RAS mutations expressed the MYC activation signature, and multiple mechanisms may be involved in activating MYC. MYC activation, whether assessed by gene expression signature or immunohistochemistry is associated with hyperdiploid MM, and shorter survival even in tumors that are not proliferative. Bortezomib treatment is able to overcome the survival disadvantage in patients with MYC activation.