Multiple Myeloma 1 Transcription Factor Is Superior to CD138 as a Marker of Plasma Cells in Endometrium.

Chronic endometritis is characterized by plasma cell (PC) infiltration of endometrial stroma. Identification of PCs can be challenging by routine hematoxylin and eosin (H&E) stain due to the low numbers of PCs or to their being obscured by other cells in the stroma. CD138 is widely used as an ancillary immunohistochemistry stain to identify PCs; however, it has a high background reaction. In this study, multiple myeloma 1 (MUM1) transcription factor is introduced as an alternative PC marker in endometrial tissues. In this study, 311 endometrial biopsies, submitted to rule out chronic endometritis, were selected. They were divided into Group I (n = 87) and Group II (n = 224). Both had MUM1 and H&E while Group I also had accompanying CD138 stains. In both groups combined, MUM1 detected plasma cells in 48% of the cases, while CD138 and H&E identified the cells in 23% and 15% of the biopsies, respectively. In addition to having a clean background, MUM1 is a more sensitive stain than CD138 for detection of PCs in endometrium.