Donna and Donald Lambert Laboratory of Myeloma Genetics at the Myeloma Institute for Research and Therapy, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA.
Previous studies have revealed that that approximately 10% to 15% of multiple myelomas (MMs) are characterized by a reciprocal t(4;14)(p16;q32) translocation that activates expression of FGFR3 and creates an IGH/MMSET fusion transcript. Current data suggest that activation of FGFR3 is the oncogenic consequence of this rearrangement. Using a combination of microarray profiling, reverse transcriptase-polymerase chain reaction (RT-PCR), and interphase fluorescence in situ hybridization (FISH), we show that 32 (18%) of 178 newly diagnosed cases of MM harbor the t(4;14)(p16;q32). Importantly, 32% of these cases lack expression of FGFR3, yet express MMSET and have an IGH/MMSET fusion transcript. Interphase FISH showed that whereas the IGH/MMSET fusion was present in more than 80% of the clonotypic plasma cells in these novel cases, there was typically a complete loss of one copy of FGFR3. These data indicate that the t(4;14)(p16;q32) and loss of FGFR3 occurred at a very early stage and suggest that activation of MMSET, not FGFR3, may be the critical transforming event of this recurrent translocation.