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). Here, MAPK3 is linked to plasma cell myeloma.