MUM1 is a B cell marker

MUM1 is a B cell marker specifically targeted at stimulated B cells with the capacity to differentiate toward plasma cells.
It is used to divide large B cell lymphomas into germinal center (MUM1 neg) and non-germinal center (MUM1 pos) phenotypes, with the former having superior outcomes (Am J Surg Pathol 2009;33:1815).
MUM1 also helps differentiate double hit lymphomas (MUM1 pos in 45%) from Burkitt and diffuse large B cell lymphoma (usually MUM1 neg).
(Am J Surg Pathol 2010;34:327).