Multiple myeloma oncogene-1 (MUM1) is a 50 kDa protein encoded by the MUM1 gene. This antibody stains MUM1 protein, which is expressed in a subset of B cells in the light zone of the germinal center, plasma cells, activated T cells and a wide spectrum of related hematolymphoid neoplasms. This antibody is useful in the sub classification of lymphoid malignancies.