BACKGROUND:Candidate biomarkers to improve venous thromboembolism (VTE) risk prediction in patients with newly diagnosed multiple myeloma (MM) undergoing anti-myeloma therapy include tissue factor-bearing microvesicles (MV-TF), procoagulant phospholipids (procoag-PPL), and D-dimer. OBJECTIVE:We aimed to determine the levels of MV-TF, procoag-PPL, and D-dimer at baseline and during initial anti-myeloma therapy and their association with the risk of VTE. METHODS:This prospective, longitudinal, observational study included 71 patients with newly diagnosed MM who were eligible for anti-myeloma therapy. Circulating MV-TF levels were measured using a functional method adapted from the Chapel Hill TF-dependent Factor Xa generation assay, and PPL and D-dimer levels with commercially available assays. The three biomarkers were measured at baseline and throughout treatment. RESULTS:Baseline and on-treatment MV-TF levels were higher in patients who developed VTE compared to those who did not (4.25 versus 2.75 fM at baseline, p = 0.047 and 6.5 versus 1.5 fM during treatment, p = 0.001). Baseline and on-treatment Procoag-PPL clotting times did not differ between the groups. Baseline D-dimer levels tended to be higher in patients who developed VTE than in those who did not (1.38 versus 0.7 μg/mL, p = 0.08). During treatment, D-dimer levels were significantly higher in the VTE group than in the non-VTE group (1.08 versus 0.44 μg/mL, p = 0.008). CONCLUSION:Our results suggest that MV-TF and D-dimer levels may help to refine VTE risk prediction in nMM patients undergoing anti-myeloma therapy. Adequately sized studies including patients receiving new MM therapies are needed to confirm this hypothesis.

Clinical determination of MP counts using flow cytometry has not been fully accepted yet due to the lack of standardization protocols. In the past 5 years, we have proposed two versions of a method with reproducible PMP counts in plasma samples. Both methods use forward scatter (FSC)-based threshold set with reference beads of appropriate sizes; first using 0.5 µm beads and later with 0.3 µm beads. Both systems provide reproducible PMP counts. However, this technique works only with some of currently used commercial flow cytometers. Instruments with limited resolution or generating heterogeneous FSC signals are excluded. Such performances are incompatible with the required interinstrument standardization. Here we show that (i) flow cytometers with sub-optimal FSC capabilities generally have higher SSC resolution and background rejection capacity, and (ii) that the same biological entities, "dim and bright PMP," both can be counted using alternative strategies, either as previously described, based on FSC measurements, or as presented here, based on SSC detection. The critical element in the standardization protocol is the use of different sizes of reference beads. This study was designed to permit simultaneous access to both FSC- and SSC-optimized platforms. A new range of about 0.17-0.6 µm eq. (µm-equivalents) is proposed for an alternative SSC-based MP gate generating the same PMP counts as those obtained in the previously proposed 0.3-1 µm eq. FSC-based MP gate. The two equivalent standardization options reconcile intrinsically different scattering behaviors between SSC- and FCS--triggered instruments and open the opportunity for multicenter studies in the future.