Similarly, CD33+ patients had significantly more immature cells (P <.001), high-risk cytogenetics (P <.001), less very good partial response (VGPR) after induction therapy (P <.001) and autologous stem cell transplantation (ASCT, P =.004) and had progressed through more than 3 treatment lines (P <.001) when compared with CD33-negative patients. 

Patients with MPC-1 negativity were more likely to have calcium levels greater than 11 (P =.048), less VGPR after ASCT (P =.029) and have progressed through more than 3 treatment lines (P =.007) compared with MPC-1–positive patients. 

Both CD33 positivity and MPC-1 negativity were associated with shorter 5-year overall survival (OS) and progression-free survival (PFS) compared with their counterparts. For CD33+ patients, the 5-year OS and PFS were lower compared with CD33- patients: 75% vs 91% (P =.04) and 48% vs 67% (p = 0.023), respectively. Similarly, MPC-1 negative patients had lower five-year OS rates and PFS compared to MPC-1+ patients: 76% vs 83% (P =.015) and 32% vs 68% (P =.002), respectively. 

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Patients who experienced at least a second or later relapse also had increasing percentages of CD33-positive (median 48.7%) and MPC-1–negative cells (median 14.1%). 

This study highlighted several key points. CD33 positivity and MPC-1 negativity appear to be associated with worse outcomes in patients with MM treated with bortezomib as induction therapy. In addition, these markers increased as patients relapsed. 

CD33 could prove to be an important drug target in future drug development based on these data. The results are limited by it taking place in a single center in a single country, which may make the results not entirely generalizable to the patients seen in the United States. 

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