Circulating plasma cells detected by flow cytometry as a predictor of survival in patients with newly diagnosed multiple myeloma.

6580 Background: The presence of circulating plasma cells (PC) detected by immunofluorescence in patients with multiple myeloma (MM) has been associated with a worse prognosis (Blood, 1996;88:1780-1787). However, PC detection by immunofluorescence, is complex and not readily available in most clinical laboratories. Therefore, we investigated the prognostic significance of circulating PC detected by flow cytometry (FC) in patients with newly diagnosed MM.,FC was performed in patients with newly diagnosed MM within the first week of diagnosis prior to the initiation of treatment. Mononuclear cells were isolated by density gradient centrifugation. The number of circulating PC was measured by gating on CD38 +, CD45- cells. 50,000 events were analyzed per patient and the number of PC detected among these events was recorded. Study endpoint was an overall survival(OS).,Between 5/1998 and 1/2003 FC was performed on 303 patients with newly diagnosed MM (123 females, 180 males). Median age was 65 yrs (range 29-94), median follow up was 24.5 mos (range 1-76). According to the International Staging System (ISS), 69 (23%), 128 (42%) and 78 (26%) patients had stage 1,2 and 3 disease respectively. In 28 patients(9%)ISS could not be determined. In 80 patients (26%) no circulating PC were seen; 163 (53%) patients had 0-5,104 (35%) patients had 6-10 circulating PC. 36 (12%) patients had > 10 circulating PC. The median OS for the whole cohort was 46 months. Patients with ≤ 5 circulating PC had median OS of 59 mo, patients with > 5 circulating PC had a median OS of 40 mo (p=0.0014). On multivariate analysis (Cox proportional hazard model), the prognostic value of circulating PC was independent of β2-microglobulin (p=0.0422), lactate dehydrogenase (p=0.0058) and C-reactive protein (p=0.0246). In patients with ISS 2 or 3, the median survival was 26 mo if there were > 5 circulating PC. Median survival was 48 mo if the circulating PC number was ≤ 5 (p=0.0244). There was no difference in survival in ISS 1 patients, however, the median OS in this group has not been reached.,The number of circulating PC measured by flow cytometry in patients with newly diagnosed MM is an independent predictor of survival. No significant financial relationships to disclose.