The enigma of ectopic expression of FGFR3 in multiple myeloma: a critical initiating event or just a target for mutational activation during tumor progression.

The t(4;14)(p16.3;q32) translocation that occurs uniquely in a subset of multiple myeloma tumors results in ectopic expression of wild-type FGFR3 and enhanced expression of MMSET, a gene that is homologous to the MLL gene that is involved in acute myeloid leukemias. Wild-type FGFR3 appears to be weakly transforming in a hematopoietic murine model, whereas FGFR3 that contains kinase-activating mutations is strongly transforming in NIH3T3 cells and the hematopoietic model. The subsequent acquisition of FGFR3 kinase-activating mutations in some tumors with t(4;14) translocations confirms a role for FGFR3 in tumor progression. However, it remains to be proven if and how dysregulation of FGFR3 or MMSET mediates an early oncogenic process in multiple myeloma.