Effect of the HDAC inhibitor vorinostat on the osteogenic differentiation of mesenchymal stem cells in vitro and bone formation in vivo.

AIM: Vorinostat, a histone deacetylase (HDAC) inhibitor currently in a clinical phase III trial for multiple myeloma (MM) patients, has been reported to cause bone loss. The purpose of this study was to test whether, and to what extent, vorinostat influences the osteogenic differentiation of mesenchymal stem cells (MSCs) in vitro and bone formation in vivo. METHODS: Bone marrow-derived MSCs were prepared from both normal donors and MM patients. The MSCs were cultured in an osteogenic differentiation induction medium to induce osteogenic differentiation, which was evaluated by alkaline phosphatase (ALP) staining, Alizarin Red S staining and the mRNA expression of osteogenic markers. Naïve mice were administered vorinostat (100 mg/kg, ip) every other day for 3 weeks. After the mice were sacrificed, bone formation was assessed based on serum osteocalcin level and histomorphometric analysis. RESULTS: Vorinostat inhibited the viability of hMSCs in a concentration-dependent manner (the IC50 value was 15.57 µmol/L). The low concentration of vorinostat (1 µmol/L) did not significantly increase apoptosis in hMSCs, whereas pronounced apoptosis was observed following exposure to higher concentrations of vorinostat (10 and 50 µmol/L). In bone marrow-derived hMSCs from both normal donors and MM patients, vorinostat (1 µmol/L) significantly increased ALP activity, mRNA expression of osteogenic markers, and matrix mineralization. These effects were associated with upregulation of the bone-specifying transcription factor Runx2 and with the epigenetic alterations during normal hMSCs osteogenic differentiation. Importantly, the mice treated with vorinostat did not show any bone loss in response to the optimized treatment regimen. CONCLUSION: Vorinostat, known as a potent anti-myeloma drug, stimulates MSC osteogenesis in vitro. With the optimized treatment regimen, any decrease in bone formation was not observed in vivo.

Continuous treatment in multiple myeloma: the future?

Major therapeutic advances in the treatment of multiple myeloma (MM) have dramatically improved response rate, remission duration and overall survival. These advances include the introduction of high-dose therapy plus autologous stem cell transplantation in younger patients and, in more recent years, the use of "novel" agents such as Thalidomide, Bortezomib, and Lenalidomide. However, despite this progress, most patient will ultimately relapse and die from resistant disease. The role of maintenance therapy in MM has been investigated for more than 30 years, but evidence of clear benefit has only recently emerged. The widely use of novel agents renewed the concept of maintenance or "continuous" treatment, after high dose therapy, as well as after conventional therapy in elderly patients. Recently, a number of randomized studies showed a benefit from maintenance therapy with these agents, including increased response rate, PFS and even OS.

Targeting the multiple myeloma hypoxic niche with TH-302, a hypoxia-activated prodrug.

Hypoxia is associated with increased metastatic potential and poor prognosis in solid tumors. In this study, we demonstrated in the murine 5T33MM model that multiple myeloma (MM) cells localize in an extensively hypoxic niche compared with the naive bone marrow. Next, we investigated whether hypoxia could be used as a treatment target for MM by evaluating the effects of a new hypoxia-activated prodrug TH-302 in vitro and in vivo. In severely hypoxic conditions, TH-302 induces G(0)/G(1) cell-cycle arrest by down-regulating cyclinD1/2/3, CDK4/6, p21(cip-1), p27(kip-1), and pRb expression, and triggers apoptosis in MM cells by up-regulating the cleaved proapoptotic caspase-3, -8, and -9 and poly ADP-ribose polymerase while having no significant effects under normoxic conditions. In vivo treatment of 5T33MM mice induces apoptosis of the MM cells within the bone marrow microenvironment and decreases paraprotein secretion. Our data support that hypoxia-activated treatment with TH-302 provides a potential new treatment option for MM.

Effectiveness and Safety of Ibrutinib for Chronic Lymphocytic Leukemia in Routine Clinical Practice: 3-Year Follow-up of the Belgian Ibrutinib Real-World Data (BiRD) Study.

The multicenter observational BiRD study investigated the real-world effectiveness and safety of ibrutinib in patients with chronic lymphocytic leukemia (CLL), mantle cell lymphoma (MCL) and Waldenström's macroglobulinemia (WM) in Belgium. This interim analysis reports results for patients with CLL, with a median follow-up of 34 months. Overall, patients had predominantly relapsed/refractory disease (73%) and were elderly (median age 72 years) with high-risk features such as del17p and/or TP53 mutations (59%). Patients were included either prospectively or retrospectively, and the total patient population effectiveness results were adjusted with left truncation. In the effectiveness population (N = 221: prospective, n = 71; retrospective, n = 150), the overall response rate was 90.0%. Median progression-free survival was 38.3 months (prospective, not estimable; retrospective, 51.5 months) and median overall survival was not yet estimable in the total, prospective and retrospective groups. Treatment-emergent adverse events (TEAEs) for the prospective and retrospective groups are reported separately. Any-grade TEAEs of interest in the prospective/retrospective groups included infections (67.1%/60.1%), diarrhea (20.5%/10.5%), hypertension (16.4%/9.8%) and atrial fibrillation (12.3%/7.2%). Major bleeding was reported in 5.5%/3.3% of prospective/retrospective patients, with little difference observed between those receiving versus not receiving antithrombotic treatment. Discontinuations due to toxicity were reported in 10.5% of patients. Results from this interim analysis show treatment with ibrutinib to be effective and tolerable, with no new safety signals observed. Future analyses will report on longer-term follow-up.

Liquid Biopsy-Derived DNA Sources as Tools for Comprehensive Mutation Profiling in Multiple Myeloma: A Comparative Study.

The analysis of bone marrow (BM) samples in multiple myeloma (MM) patients can lead to the underestimation of the genetic heterogeneity within the tumor. Blood-derived liquid biopsies may provide a more comprehensive approach to genetic characterization. However, no thorough comparison between the currently available circulating biomarkers as tools for mutation profiling in MM has been published yet and the use of extracellular vesicle-derived DNA for this purpose in MM has not yet been investigated. Therefore, we collected BM aspirates and blood samples in 30 patients with active MM to isolate five different DNA types, i.e., cfDNA, EV-DNA, BM-DNA and DNA isolated from peripheral blood mononucleated cells (PBMNCs-DNA) and circulating tumor cells (CTC-DNA). DNA was analyzed for genetic variants with targeted gene sequencing using a 165-gene panel. After data filtering, 87 somatic and 39 germline variants were detected among the 149 DNA samples used for sequencing. cfDNA showed the highest concordance with the mutation profile observed in BM-DNA and outperformed EV-DNA, CTC-DNA and PBMNCs-DNA. Of note, 16% of all the somatic variants were only detectable in circulating biomarkers. Based on our analysis, cfDNA is the preferable circulating biomarker for genetic characterization in MM and its combined use with BM-DNA allows for comprehensive mutation profiling in MM.

Real-world data confirming the efficacy and safety of decitabine in acute myeloid leukaemia - results from a retrospective Belgian registry study.

Objectives: Currently, there is no standard treatment for patients with acute myeloid leukaemia (AML) ineligible for standard induction chemotherapy (IC). This study aimed to report real-world evidence data on the efficacy and safety of decitabine in this patient group.Methods: This study was a Belgian, retrospective, non-interventional, multicentre registry of patients ≥ 65 years, with newly-diagnosed de novo or secondary AML ineligible for IC. Patients were treated according to routine clinical practice. Overall survival (OS), progression-free survival (PFS) and transfusion independence for ≥8 consecutive weeks were evaluated.Results: Forty-five patients were enrolled, including 67% (n = 30) with secondary AML. Median OS and PFS were 7.3 months (95% CI: 2.2-11.1) and 4.1 months (95% CI: 2.1-7.6) respectively. A subpopulation analysis showed that patients treated with ≥4 cycles (n = 21) had significantly better outcomes compared to patients receiving <4 cycles (median OS 17.5 vs 1.6 months; median PFS 17.5 vs. 1.4 months). Twenty-five percent and 58% of patients that were respectively RBC or platelet transfusion-dependent at baseline became transfusion independent during treatment.Conclusion: This real-world data confirms that decitabine can lead to transfusion independence and longer OS in AML patients, particularly after administering ≥4 cycles, as indicated in the summary of product characteristics.

Epigenetic silencing of the tetraspanin CD9 during disease progression in multiple myeloma cells and correlation with survival.

PURPOSE: The purpose of this study was to investigate expression and epigenetic regulation of CD9 in multiple myeloma (MM) cells during disease progression. EXPERIMENTAL DESIGN: CD9 expression was retrospectively analyzed on bone marrow myeloma samples from 81 patients by immunophenotyping. CD9 expression by murine 5TMM cells was detected by flow cytometric staining and quantitative PCR. The methylation status of the CD9 promoter was determined by bisulfite PCR sequencing. RESULTS: Primary plasma cells in the majority of MM patients with nonactive disease (n = 28) showed CD9 expression, whereas most cases with active disease (n = 53) were CD9 negative. CD9 expression in diagnostic bone marrow samples (n = 74) correlated with survival. Moreover, CD9 expression on murine 5T33 and 5T2MM cells was significantly down-regulated during disease development. Treatment of CD9-nonexpressing 5T33MMvt cells with the clinically relevant histone deacetylase inhibitor LBH589 resulted in a significant increase in CD9 expression. In contrast, cells treated with the demethylation agent 5-aza-2'deoxycytidine barely showed any increase. A combination study with both compounds resulted in a strong synergistic reactivation of CD9. CD9-expressing 5T33MMvv cells and 5T33MMvt cells stably transduced with a mCD9 lentiviral transferplasmid were shown to be more susceptible to natural killer cell-mediated cytolysis than CD9-negative 5T33MMvt cells. CONCLUSIONS: CD9 expression correlates with disease status and survival of MM patients. In the murine 5T33MM model, we show that histone modifications, and to a lesser extent CpG methylation, are key epigenetic events in CD9 down-regulation. Furthermore, as CD9 expression becomes down-regulated, 5T33MM cells become less susceptible to natural killer cell-mediated cytolysis.

The Transfer of Sphingomyelinase Contributes to Drug Resistance in Multiple Myeloma.

Multiple myeloma (MM) is well-known for the development of drug resistance, leading to relapse. Therefore, finding novel treatment strategies remains necessary. By performing a lipidomics assay on MM patient plasma, we aimed to identify new targets. We observed a dysregulation in the sphingolipid metabolism, with the upregulation of several ceramides and downregulation of sphingomyelin. This imbalance suggests an increase in sphingomyelinase, the enzyme responsible for hydrolyzing sphingomyelin into ceramide. We confirmed the upregulation of acid sphingomyelinase (ASM) in primary MM cells. Furthermore, we observed an increase in ASM expression in MM cell lines treated with melphalan or bortezomib, as well as in their exosomes. Exosomes high in ASM content were able to transfer the drug-resistant phenotype to chemosensitive cells, hereby suggesting a tumor-protective role for ASM. Finally, inhibition of ASM by amitriptyline improved drug sensitivity in MM cell lines and primary MM cells. In summary, this study is the first to analyze differences in plasma lipid composition of MM patients and match the observed differences to an upregulation of ASM. Moreover, we demonstrate that amitriptyline is able to inhibit ASM and increase sensitivity to anti-myeloma drugs. This study, therefore, provides a rational to include ASM-targeting-drugs in combination strategies in myeloma patients.

Extravasation and homing mechanisms in multiple myeloma.

Multiple myeloma (MM) is a malignant B-cell disorder characterized by a monoclonal expansion of plasma cells (PC) in the bone marrow (BM). During the main course of disease evolution, MM cells depend on the BM microenvironment for their growth and survival. Reciprocal interactions between MM cells and the BM mediate not only MM cell growth, but also protect them against apoptosis and cause bone disease and angiogenesis. A striking feature of MM represents the predominant localization and retention of MM cells in the BM. Although BM PC indeed represent the main neoplastic cell type, small numbers of MM cells can also be detected in the peripheral blood circulation. It can be assumed that these circulating cells represent the tumour-spreading component of the disease. This implicates that MM cells have the capacity to (re)circulate, to extravasate and to migrate to the BM (homing). In analogy to the migration and homing of normal leucocytes, the BM homing of MM cells is mediated by a multistep process of extravasation with adhesion to the endothelium, invasion of the subendothelial basement membrane, followed by further migration within the stroma, mediated by chemotactic factors. At the end stage of disease, MM cells are thought to develop autocrine growth supporting loops that enable them to survive and proliferate in the absence of the BM microenvironment and to become stroma-independent. In this stage, the number of circulating cells increases and growth at extramedullary sites can occur, associated with alteration in adhesion molecule and chemokine receptor expression. This review summarizes the recent progress in the study of the extravasation and homing mechanisms of MM cells.

Multiple myeloma--an update on diagnosis and treatment.

Multiple myeloma is a plasma cell (PC) malignancy characterized by the accumulation of monoclonal PCs in the bone marrow and the production of large amounts of a monoclonal immunoglobulin or paraprotein. In the past years, new approaches in the diagnosis and treatment were introduced aiming to identify high-risk patients who need proper anti-myeloma treatment. Intensive therapy including autologous hematopoietic stem cell transplantation and the new agents bortezomib, thalidomide, and lenalidomide have improved patients' responses. Further optimalization of the different treatment schedules in well-defined patient groups may prolong their survival. Patient stratification is currently based on patient characteristics, extent of myeloma disease, and associated cytogenetic and laboratory anomalies. More and more gene expression studies are introduced to stratify patients and to individualize therapy.

Migration of culture-expanded human mesenchymal stem cells through bone marrow endothelium is regulated by matrix metalloproteinase-2 and tissue inhibitor of metalloproteinase-3.

BACKGROUND AND OBJECTIVES: Mesenchymal stem cells (MSC) are adult stem cells that can be expanded many fold in vitro and have the therapeutic potential to restore the bone marrow microenvironment and support hematopoietic recovery after myeloablative conditioning for hematopoietic stem cell transplantation. Successful homing to the target tissue, such as bone marrow, implies that MSC are able to extravasate after systemic administration. However, the extravasation capacity of MSC and the underlying mechanisms are poorly understood to date. We studied in vitro the capacity of MSC to migrate through bone marrow endothelium. DESIGN AND METHODS: In vitro invasion and transendothelial migration assays were performed. The expression of matrix metalloproteinase (MMP) was analyzed by reverse transcriptase polymerase chain reaction (RT-PCR) and zymography. Migration of cells cultured at high or low confluence was compared and differential gene expression in these conditions was analyzed with microarray and real-time RT-PCR. The functional involvement in MSC migration was assessed using neutralizing anti-MMP-2 antibody, MMP-2 short interfering RNA or recombinant tissue inhibitor of metalloproteinase (TIMP-3). RESULTS: We demonstrated that MSC can invade reconstituted basement membrane and that bone marrow endothelial cells stimulate this process. We also showed that the transendothelial migration of MSC is at least partially regulated by MMP-2. High culture confluence was found to increase production of the natural MMP-inhibitor TIMP-3 and decrease transendothelial migration of MSC. INTERPRETATION AND CONCLUSIONS: We show that MSC have the potential to migrate through bone marrow endothelium and that this process involves MMP-2. Moreover, the migration of MSC is significantly influenced by the level of culture confluence. Increased culture confluence impairs migration and is related to an upregulation of TIMP-3. The therapeutic use of MSC would benefit from a selection of culture conditions that allow optimal extravasation of these cells.

Clinical significance of chemokine receptor (CCR1, CCR2 and CXCR4) expression in human myeloma cells: the association with disease activity and survival.

BACKGROUND AND OBJECTIVES: The capacity of multiple myeloma (MM) cells to home to and reside in the bone marrow implies that they must be equipped with appropriate adhesion molecules and chemokine receptors to allow transendothelial migration. We and others have previously shown that human MM cells express at least three different chemokine receptors that are functionally involved in MM cell migration, i.e. CCR1, CCR2 and CXCR4. In this study, we analyzed the surface expression of these chemokine receptors on primary MM cells from bone marrow samples. DESIGN AND METHODS: Chemokine receptor expression was analyzed on bone marrow samples from a large population of patients (n=80) by flow cytometric analysis. The chemokine receptor expression profile was compared with clinical characteristics. Statistical significance was evaluated by Fisher's exact test. Survival curves were constructed using the Kaplan-Meier method. Cox regression analysis was used to determine the effect of chemokine receptor expression on survival. RESULTS: A heterogeneous expression pattern was observed for the three receptors tested. The chemokine receptor status (CRS) (i.e. no expression versus expression of at least one chemokine receptor), as well as expression of individual chemokine receptors was analyzed in relation to clinical and laboratory features and evaluated for prognostic significance. Chemokine receptor expression was significantly inversely correlated with disease activity: patients with active disease showed a significantly lower expression of CCR1, CCR2, as well as CXCR4 as compared to patients with non-active disease. Furthermore, the chemokine receptor expression profile correlated with serum beta2-microglobulin, C-reactive protein and hemoglobin. CRS, and the individual expressions of CCR1, CCR2 and CXCR4 in diagnostic bone marrow samples (n=70) correlated with survival. Multivariate analysis, using the Cox proportional hazard regression model, identified CRS, along with serum beta-microglobulin, as an independent prognostic factor. INTERPRETATION AND CONCLUSIONS: This study indicates that the chemokine receptor expression profile of MM cells correlates with disease status and survival of MM patients. This observation might reflect impaired chemoattraction and retention of MM cells within the bone marrow microenvironment, resulting in disease progression.

The involvement of stromal derived factor 1alpha in homing and progression of multiple myeloma in the 5TMM model.

BACKGROUND AND OBJECTIVES: Multiple myeloma (MM) is a lethal plasma cell cancer characterized by the monoclonal growth of cells in the bone marrow. To reach the bone marrow, MM cells need to be attracted by chemokines. Recently, it has been shown that chemokines can also be involved in the growth of several cancer types. Stromal cell derived factor 1a (SDF1alpha) or CXCL12 is known to play an important role as a chemokine for hematopoietic progenitor cells and human MM cells. We studied the effects of SDF1a in the 5TMM murine model. DESIGN AND METHODS: The in vitro effects of SDF1alpha were analyzed by gelatin zymography, adhesion, migration, proliferation, and chemoinvasion assays and by blockade with the CXCR4 inhibitor, 4F-benzoyl-TN14003. In vivo, diseased mice were treated with either vehicle or 4F-benzoyl-TN14003. RESULTS: In vitro SDF1alpha was capable of attracting both 5T2MM and 5T33MM cells and inducing a 1.6-fold increase in MMP9 production by the 5TMM cells, which was correlated with an increased invasive capacity. In addition, SDF1alpha induced a 20% increase in DNA synthesis in the 5TMM cells. All these effects could be blocked by the CXCR4 inhibitor, 4Fbenzoyl- TN14003. An in vivo study in the 5T33MM model showed that blocking CXCR4 led to a 20% reduction in bone marrow tumor load. INTERPRETATION AND CONCLUSIONS: These data demonstrate that SDF1alpha/CXCR4 is involved in the homing and the expansion of MM cells. Blocking CXCR4 could be useful in synergy with other anti-neoplastic treatments targeting the bone marrow microenvironment.

Biomarker Analysis in a Phase II Study of Sunitinib in Patients with Advanced Melanoma.

AIM: To investigate the efficacy of sunitinib in patients with advanced melanoma and to correlate angiogenic biomarkers with response and survival. PATIENTS AND METHODS: We performed a phase II study in patients with advanced pre-treated melanoma. The primary endpoint was tumor response. Blood samples for biomarker analysis including vascular endothelial growth factor (VEGF), and its receptors VEGFR1 and -2, placental growth factor (PlGF) and circulating endothelial cells (CEC) were collected at baseline and during the first cycle. RESULTS: Four out of 39 patients (13%) achieved a partial response and eight (26%) stable disease. Time to progression was at least six months in seven patients. High baseline VEGFR1 levels and high baseline PlGF levels were both associated with a non-significant worse survival (p=0.08 for both). CONCLUSION: Sunitinib demonstrates limited activity in unselected patients with refractory advanced melanoma, but a minority of patients experienced long-term disease control. Identification of these patients remains a challenge.

Mechanisms involved in the differential bone marrow homing of CD45 subsets in 5T murine models of myeloma.

Multiple myeloma (MM) is an incurable plasma cell cancer, localized in the bone marrow (BM). The mechanisms used by these cells to (re-)enter this organ remain largely unknown. Recently, we reported that both CD45+ and CD45- myeloma cells home to the BM and induce myeloma disease. In this work, we investigated the underlying mechanisms involved in the homing of CD45+ and CD45- myeloma cells in the experimental 5T2MM and 5T33MM murine models. In vivo tracing of flow cytometric sorted and radioactively labeled CD45 subsets revealed a reduced homing of the CD45- 5TMM cells to the BM as compared to the CD45+ 5TMM cells. Migration assays demonstrated an impaired chemotaxis towards BM endothelial cell conditioned medium, BM stromal cell conditioned medium and towards the basement membrane component laminin-1 of the CD45- 5TMM cells compared to the CD45+ subset. Matrix metalloproteinase-9 (MMP-9) and urokinase type plasminogen activator (uPA) are key extracellular matrix proteases involved in the invasion of cancer cells. Inhibitor and antibody blocking experiments demonstrated the involvement of both in the invasion of the 5TMM cells. CD45- 5TMM cells had a low secretion of MMP-9 and (for the non-aggressive line 5T2MM only) a low cell surface expression of uPA receptor, as revealed by gelatin zymography and flow cytometric analysis, respectively. Accordingly, the synthetic basement membrane invasive capacity of the CD45- 5TMM subpopulations was also impaired. Our results indicate that CD45+ and CD45- 5T myeloma cells have a differential BM homing attributable to differential migratory and invasive capacities.

Monocyte chemoattractant protein-1 (MCP-1), secreted by bone marrow endothelial cells, induces chemoattraction of 5T multiple myeloma cells.

Homing of multiple myeloma (MM) cells to the bone marrow (BM) requires transendothelial migration. In the present work we tested whether monocyte chemoattractant protein-1 (MCP-1) and CCR2, the high affinity receptor for MCP-1, are involved in this process. Murine 5T2 and 5T33MM cell lines were selected as source of MM cells and STR4, 10 and 12 of BM endothelial cells (BMEC). RT-PCR demonstrated transcripts for MCP-1 in BMEC and ELISA the presence of MCP-1 protein in culture medium. RNase protection assay showed mRNA expression for CCR2, and FACS analysis the presence of CCR2 protein on the MM cells. EC conditioned medium induced chemoattraction of MM cells, a phenomenon inhibited by anti-MCP-1 antibodies. In conclusion, MM cells express CCR2 and are attracted by MCP-1 secreted by BMEC. We suggest that local MCP-1 production by BMEC is one of the mechanisms involved in homing of myeloma cells to the BM.

Upregulation of miR-135b is involved in the impaired osteogenic differentiation of mesenchymal stem cells derived from multiple myeloma patients.

Previous studies have demonstrated that mesenchymal stem cells from multiple myeloma (MM) patients (MM-hMSCs) display a distinctive gene expression profile, an enhanced production of cytokines and an impaired osteogenic differentiation ability compared to normal donors (ND-hMSCs). However, the underlying molecular mechanisms are unclear. In the present study, we observed that MM-hMSCs exhibited an abnormal upregulation of miR-135b, showing meanwhile an impaired osteogenic differentiation and a decrease of SMAD5 expression, which is the target of miR-135b involved in osteogenesis. By gain and loss of function studies we confirmed that miR-135b negatively regulated hMSCs osteogenesis. We also found that MM cell-produced factors stimulated ND-hMSCs to upregulate the expression of miR-135b. Importantly, treatment with a miR-135b inhibitor promoted osteogenic differentiation in MM-hMSCs. Finally, we observed that MM cell-derived soluble factors could induce an upregulation of miR-135b expression in ND-hMSCs in an indirect coculture system and the miR-135b expression turned to normal level after the removal of MM cells. Collectively, we provide evidence that miR-135b is involved in the impaired osteogenic differentiation of MSCs derived from MM patients and might therefore be a promising target for controlling bone disease.

Diagnosis and follow-up of monoclonal gammopathies of undetermined significance; information for referring physicians.

The prevalence of monoclonal gammopathy of undetermined significance (MGUS) is generally estimated at 3.4% in the general population over 50 years, and its incidence increases with age. MGUS represents a preneoplastic entity that can transform into multiple myeloma or other lymphoproliferative disorders. The risk of malignant transformation is estimated at 1% per year and persists over time. Predictors of malignant transformation have been identified such as the heavy chain isotype, The level of monoclonal proteins, increasing levels of the monoclonal component during the first years off follow-up, the percentage of bone marrow plasmocytosis, the dosage of serum free light chains, the presence of immunophenotypically abnormal plasma cells, aneuploidy, and the presence of circulating plasma cells. Prognostic scores that combine certain of these factors have been proposed and allow the identification of high-risk patients. Their use could assist in tailoring the care for each patient, based on his/her risk profile.

Effect of sample dilution on serum free light chain concentration by immunonephelometric assay.

BACKGROUND: Free light chains (FLC) are useful biomarkers in the assessment of plasma cell disorders. Concerns have been raised about some technical aspects of the assay. This report examined the occurrence of dilution anomalies and/or antigen excess. METHODS: FLC were determined on a BNII instrument at at-least two dilutions (100- and 2000-fold) in 2088 consecutive samples from 865 different patients. In part of them, the 400-fold dilution was also available. RESULTS: Higher than 2-fold differences and inconsistencies ["<" or ">" result at one dilution not consistent with the result obtained at another dilution] between the 100- and 2000-fold dilutions were found in 12.7% of patients for κ FLC and in 3.1% of patients for λ FLC. More than 4-fold differences between results obtained at the 2000-fold and the 100-fold dilutions were observed in 5.4% of patients for κ FLC and in 1.2% of patients for λ FLC. CONCLUSIONS: The FLC assay on BNII suffers from sample dilution anomalies and/or failure of antigen excess detection in a substantial fraction of patients. Laboratory professionals and clinicians should be alert to such analytical difficulties.