Multiparameter flow cytometry for staging of solitary bone plasmacytoma: New criteria for risk of progression to myeloma

Solitary plasmacytoma represents a heterogeneous group of patients; approximately half develop multiple myeloma (MM) in 2 or 3 years,whereas others remain disease-free at 10 years. By definition, these patients do not have morphologic bone marrow (BM) plasma cell (PC) infiltration. Here, we investigated whether sensitive BM evaluation of patients withsolitaryboneplasmacytoma(SBP; n = 35) andextramedullary plasmacytoma (EMP; n = 29) through multiparameter flow cytometry (MFC) would unravel the presence of clonal PCs in otherwise disease-free BM, and whether BMclonality predicted higher risk of progression. BMclonal PCs were detected in 17 of 35 SBP (49%) and 11 of 29 EMP (38%) patients. Seventy-one percent of flow-positive vs only 8% of flow-negative SBP patients evolved to MM (median time to progression of 26 months vs not reached; hazard ratio, 17.4; P < .001). No significant differences were observed among EMP cases. Our results highlight the importance of MFC for sensitive BM evaluation of SBP patients, to predict risk of developing treatment-requiring MM and to plan disease monitoring.This work was supported by the Cooperative Research Thematic Network grants RD12/0036/0058, RD12/0036/0069 and RD12/0036/0052 of the Red de Cancer (Cancer Network of Excellence), Instituto de Salud Carlos III, Spain, Instituto de Salud Carlos III/Subdirección General de Investigación Sanitaria (FIS: PI060339, 06/1354, 02/0905, 01/0089/01-02, PS09/01897/01370, G03/136, Sara Borrell: CD13/00340), Consejería de Educacion, Junta de Castilla y León Valladolid, Spain (HUS396A12-1), and Asociación Española Contra el Cáncer (AECC, GCB120981SAN), Spain.Peer Reviewe