The MUM1 (Multiple Myeloma Oncogene 1) gene was originally identified because of its involvement in the t(6,14) translocation observed in multiple myeloma, which causes juxtaposition of the MUM1 gene to the Ig heavy-chain locus. MUM1 is expressed in a wide spectrum of lymphoid neoplasms but not in myeloid and extra-hematopoitic tumors. MUM1 is a valuable marker for understanding and characterizing histogenesis of B-cell lymphomas. It is an excellent marker for Hodgkin's and Reed-Sternberg cells of classic Hodgkin's disease in combination with CD30.Synonyms: Interferon regulatory factor 4, LSIRF, Lymphocyte-specific interferon regulatory factor, MUM1, Multiple myeloma oncogene 1, NF-EM5