ERBB4 and plasma cell myeloma: Besides, NRG3 has been reported to be significantly overexpressed by myeloma cells as compared to other cells in the BM microenvironment [20]. In this study, we show that pMSCs co-cultured with myeloma cells also secrete NRG3, which is able of activating ErbB4 and to promote myeloma proliferation, thereby creating a paracrine amplification loop for myeloma growth.