Hematopoietic cells expressingthe hypermorphic Rad50s allele show hematopoieticfailure, which can be mitigated by the lack of a transcription factor, Mef/Elf4.However, we find that 70% ofMef−/−Rad50s/smice die from multiple myeloma or other plasma cell neoplasms. This evidence concerns the gene ELF4 and plasma cell myeloma.