Hevylite®, a New Marker of Tumor Measurement In Waldenstrom Macroglobulinemia

Waldenstrom macroglobulinemia (WM) is a low grade B cell lymphoma characterized by bone marrow infiltration of lymphoplasmacytic tumor cells that secrete monoclonal IgM (M-protein) into the serum. Measurement of the serum M-protein [using serum protein electrophoresis (SPEP)] and measurement of total IgM (using nephelometry) are used to diagnose and monitor WM. There are, however, many limitations with these techniques and new markers are needed. IgG and IgA Hevylite® immunoassays have been reported to be more sensitive than SPEP and nephelometry for identifying monoclonal immunoglobulins in multiple myeloma and unlike immunofixation, provide quantitative information. We hypothesized that serum IgM Hevylite assays (specifically measuring IgMkappa and IgMlambda, separately) would accurately identify serum IgM M-proteins. We also evaluated the association between known tumor burden markers and prognostic factors with IgM Hevylite results in patients with WM.

We retrospectively measured IgMkappa and IgMlambda in sera from 59 WM patients: 44 patients were at diagnosis and 15 had relapsed disease. The diagnosis of WM was made according to the current guidelines. All serum samples were kept frozen in the Lille serum bank since collection. All patients gave informed consent prior to the collection and none were treated at time of collection of the serum. Approval of this protocol was obtained from the CHRU Lille and was in accordance with the Declaration of Helsinki.

Hevylite measurements were made at The Binding Site Ltd, Birmingham, UK. A normal range was produced from normal (blood donor) sera (n=120), median (and 95%ile ranges) were; IgMkappa 0.634g/L (0.29-1.82), IgMlambda 0.42g/L (0.17-0.94), IgMkappa/IgMlambda ratio 1.6 (0.95-2.3). For ease of comparison IgM hevylite ratios were expressed as the involved monoclonal immunoglobulin/uninvolved polyclonal immunoglobulin (IgMi). To describe the distribution of IgMi Hevylite levels in patients with WM, the median and range (min-max) were reported. Median values were compared using the Wilcoxon rank-sum test and ANOVA. Fisher's exact test was used to compare proportions. All statistical tests were two-sided. All analyses were conducted using SPSSv12 software.

The baseline characteristics of the patients were as follows: the median (range) age was 68 years (41-86), male/female 38/21, serum b2M 3.0mg/L (1.2-9.0), hemoglobin 11.8g/dL (7.6-15.4), platelet count 267 ×10⁹/mm³ (55-741), serum M-spike 19g/L (3.0-52.7). In our series, 18 (31%), 22 (37%) and 19 (32%) patients had low, intermediate and high risk disease respectively, in the WM-IPSS scoring system. The median (min-max) IgMkappa ratio was 134 (8.7-2850) and IgMlambda ratio was 0.03 (0.0007-0.39). IgMi Hevylite ratio was 98.07 (2.59-2850). The IgMi Hevylite correlated well with the M-spike measured using SPEP (r=0.601, p<0.0001).

In our study, high IgMi Hevylite levels correlated well with markers of high tumor burden and of poor prognosis. The median (range) IgMi Hevylite level was higher in patients with hemoglobin <10g/dL versus ≥10 g/dL, 267 (8.1-1722) and 76 (2.6-2850) respectively (p=0.013). The median (range) IgMi Hevylite ratio level was significantly (p=0.033) higher in the high risk IPSS group 208 (2.6-2850) than in the intermediate 75 (15-1033) and low risk groups, 98 (8-571).

The IgMi Hevylite levels also separated WM patients with progressive disease who required therapy. Twenty seven pts were symptomatic and required specific treatment for WM, and 32 pts were left untreated. The median IgMi Hevylite ratio was significantly higher in progressing patients, 210 (8.1-2850) and 60 (2.6-571) in the 2 groups, respectively (p=0.014).

In this study we demonstrated that IgM Hevylite measurement is a new and reliable marker for monitoring WM disease. It is related to poor prognostic markers that separate WM patients with progressive disease who require therapy. We are currently expanding the cohort to confirm these observations. These findings have implications in the management of patients with WM.

Leblond:Roche: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Mundipharma: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Genzyme: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees. Leleu:Celgene: Consultancy, Research Funding; Janssen Cilag: Consultancy, Research Funding; Leo Pharma: Consultancy; Amgen: Consultancy; Chugai: Research Funding; Roche: Consultancy, Research Funding; Novartis: Consultancy, Research Funding.