Quantification of clonal circulating plasma cells in relapsed multiple myeloma.

The presence of clonal circulating plasma cells (cPCs) remains a marker of high-risk disease in newly diagnosed multiple myeloma (MM) patients. However, its prognostic utility in MM patients with previously treated disease is unknown. We studied 647 consecutive patients with previously treated MM seen at the Mayo Clinic, Rochester who had their peripheral blood evaluated for cPCs by multi-parameter flow cytometry. Of these patients, 145 had actively relapsing disease while the remaining 502 had disease that was in a plateau and included 68 patients in complete remission (CR) and 434 patients with stable disease. Patients with actively relapsing disease were more likely to have clonal cPCs than those in a plateau (P < 0·001). None of the patients in CR had any clonal cPCs detected. Among patients whose disease was in a plateau, the presence of clonal cPCs predicted for a worse median survival (22 months vs. not reached; P = 0·004). Among actively relapsing patients, the presence of ≥100 cPCs predicted for a worse survival after flow cytometry analysis (12 months vs. 33 months; P < 0·001). Future studies are needed to determine the role of these findings in developing a risk-adapted treatment approach in MM patients with actively relapsing disease.