MPC-1 expression in myeloma cells is associated with the efficacy of bortezomib therapy

The use of bortezomib in the clinic has significantly improved outcomes for patients with multiple myeloma (MM), even those harboring high-risk cytogenetic abnormalities or those classified in the high-risk category according to the International Staging System (ISS). In this study, we analyzed the association between immunophenotyping on myeloma cells and the clinical outcomes of patients who received bortezomib-based regimens as first-line therapy. Immunophenotypic analysis before bortezomib therapy was performed by flow cytometry, and whether the immunophenotyping results influenced the clinical outcomes of the patients was investigated. Seventy-four newly diagnosed patients with MM were included in this study. We found that the expression of MPC-1 significantly predicted the time to next therapy (TNT), with a longer TNT in the MPC-1 positive group (p=0.005), whereas it did not affect overall survival (OS; p=0.773). In addition, we found that CD45-positivity was associated with shorter TNT (p=0.0432). Following ISS assessment at treatment initiation, patients who were classified as stage I showed a slightly longer OS compared to those at stage II or III; however, these results were not significant (p=0.0987). Furthermore, multivariate analysis revealed the prognostic significance of MPC-1 expression, as MPC-1-negativity was associated with a worse TNT. The combination of MPC-1 and CD45 status more sensibly predicted the TNT for bortezomib therapy. Our results demonstrate the clinical importance of immunophenotyping on myeloma cells to determine patient prognoses in this era of novel therapeutic agents.