STAT3 and plasma cell myeloma: We then examined several signaling pathways in MSCs, and we observed increased phosphorylation of extracellular signal–regulated kinase 1/2 (ERK1/2), signal transducer and activator of transcription (STAT) 1, STAT3, and Akt in MSCs cocultured with myeloma cells than those in MSCs alone (Figure 4B).