CD9 and plasma cell myeloma: By MTS analysis we also found that after pretreatment of 5-Aza, the sensitivity to bortezomib in U266 and NCI-H929 raised significantly while the bortezomib sentitive RPMI8226 raised a little bit (Figure 2), suggesting the synergistic interaction of 5-Aza and bortezomib inhibition in multiple myeloma may due to CD9 expression reversion.