IgA Hevylite® Test As a Surrogate to Serum Protein Electrophoresis (SPEP) or Nephelometry in the Management of IgA Myeloma
Authors: Boyle Eileen Mary , Young Philip , Demarquette Helene , Gay Julie , Debarri Houria , Bonnet Sarah , Herbaux Charles , Dulery Remy , Manier Salomon , Faucompre Jean-Luc , Combat Frederic , Pietrantuono Annie , Onraed Brigitte , Hennache Bernadette , Facon Thierry , Harding Stephen J , Leleu Xavier 
Published: October 2019

Abstract
Abstract 3970

Background:
Measurement of serum M-spike is used to assess response to therapy and treatment-free survival in IgA myeloma. However, its resolution on SPEP and the presence of IgA-dymers can make accurate measurement difficult. The more the M-spike decreases on SPEP, the more imprecise the M-spike measurement is using SPEP. IgA M-spike often migrates in the betaglobines that renders the M-spike measurement often complicated to analyze. Furthermore, quantification of the clonal IgA chain by nephelometry (IgAneph), which inherently includes monoclonal and polyclonal immunoglobulins, does not accurately reflect the tumour burden. Currently, there is a need in myeloma with IgA isotype (approximately 30–40% of patients) to identify new markers that better reflect the disease burden and the response to treatment, and correlate to patients' outcome. Hevylite® measures IgAkappa and IgAlambda and might provide precise quantitative measurement of the IgA M-spike. We sought to determine whether Hevylite® can be used as a reliable marker for diagnosis and response to therapy in IgA myeloma as compared to the M-spike measurement on SPEP and nephelometry.

Methods:
We conducted a retrospective analysis on 113, smoldering or symptomatic, IgA myeloma patients at diagnosis referred to our department from 1997 to 2011. All serum samples were collected prior to treatment or at relapse (for sequential data) and were kept frozen since collection. Hevylite® measurements were made at The Binding Site Ltd, Birmingham, UK. A normal range was produced from normal (blood donor) sera (n=138), and were for IgA kappa 0.48–2.82g/L, IgA lambda 0.36–1.98g/L and IgA K/L ratio 0.80–2.04. For ease of comparison we have studied the IgA hevylite ratios expressed as IgA K/L ratio.

Results:
The median age at diagnosis was 65 years (range: 33–93) and the M/F sex ratio was 0,91. Forty-eight percent of patients had an ISS greater than 2 (n=86). On nephelometry the median IgA level was 22g/L (range min-max, 0–100). Fifty patients had M-spikes migrating among the betablobulines, 27 among the gammaglobulines, 10 migrated in both and 23 unspecified. Fourteen patients had oligosecretory disease (M-component < 10g/L). Forty-two patients had an IgA kappa clonal chain, 70 others an IgA lambda and for one patient the data was not available. Among IgA kappa patients the mean HCLratio was 616.6 (median 117.7 [0.021–4323.7]) whereas it was 0.61 (0.21 [0.004–0.455]) among the IgA lambda patients.
Across the entire population, 58 patients were identified by SPEP and HCL ratios. Among the 55 patients whose M-component was not quantified on SPEP, HCL ratios were abnormal in 53/55 (96%) cases. In the subgroup of patients whose M-protein migrates in the beta-region 29 out of 50 are identified by HCL ratios and SPEP. Another 19 patients (38%) had abnormal HCL ratios while unquantified on SPEP. The same was seen in patients whose M-protein migrates among the gammaglobulins with 16/27 and 11/27 (40%), respectively. In the last subgroup of patients with beta and gamma migrating M-proteins, all (10/10) were identified by HLC and SPEP. More interestingly, among the oligosecretory MM patients identified by an M-component < 10g/L, all (14 patients) had an abnormal HCL ratio. In our series of IgA myeloma, 51% of patients were accurately quantified on SPEP. When using HCLratios, an extra 47% of patients became measurable, with an abnormal HLC ratios allowing IgA myeloma in up to 98% of cases.
When considering IgA measurement using nephelometry, 102 patients had both high IgA levels (90%) and abnormal HCL ratios. Interestingly, 7 patients had normal IgA levels with IgAneph and abnormal HCL ratio offering a useful diagnostic tool for 96% of patients as compared to IgAneph.
In our series, IgA myeloma was neither associated with a poor outcome (median [range] OS: 119 months [0,5–604]) nor a poor response to therapy (median [range] TTP: 16 months (1–92). HCL involved chain ROC analysis identified a 37g/L cut-off as prognostic in IgA myeloma(p=0.039).

Conclusion:
Hevylite® is a new and reliable marker for diagnostic and monitoring of IgA myeloma. It enables to quantify accurately up to 98% of IgA-MM patients. These preliminary data need confirmation in further prospective trials in order to monitor further the impact of this marker in IgA myeloma patients before it becomes the gold standard to monitor the IgA M-protein in years to come.

Disclosures:
Boyle: Chugai: Consultancy, Honoraria. Combat:The Binding Site: Employment. Pietrantuono:The Binding Site: Employment. Facon:onyx: 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; millenium: Membership on an entity's Board of Directors or advisory committees. Harding:The Binging Site: Employment. Leleu:Celgene: Honoraria, Research Funding, Speakers Bureau; Janssen: Honoraria, Research Funding, Speakers Bureau; Novartis: Honoraria, Research Funding; Amgen: Honoraria, Research Funding; Sanofi: Honoraria; Onyx: Honoraria, Speakers Bureau; LeoPharma: Honoraria, Speakers Bureau.