The utility of intact light chain mass spectrometry-based assays for the detection of plasma cell disorders and the assessment of treatment responses

Abstract

Mass spectrometry (MS) assays have been emerging over the last few years as a new and potentially more sensitive way to track monoclonal proteins in the serum patients with plasma cell disorders (PCD), although limited data on their prognostic utility is available. In addition, no studies have explored their potential utility in patients with multiple myeloma with low-level monoclonal protein production. Despite the use of intact light chain MS-based assays in lieu of immunofixation being approved by the Internal Myeloma Working Group in 2021, MS testing to monitor patients with PCD is currently only available at a single institution who have developed an in-house test. This thesis presents work undertaken alongside the Binding Site Ltd to develop a regulatory approved intact light chain MS-based assay and clinical studies undertaken independently to assess the utility of this assay for monitoring patients with PCD. Assay optimisation work conducted as part of this thesis has shown that the combination of free light chain (FLC) specific reagents in addition to a five bead matrix-assisted laser desorption/ionisation time-of-flight MS (MALDI-TOF MS) assay provides a more sensitive panel for the detection of low-level residual monoclonal FLC. However, the application of MALDI-TOF MS to urine did not provide any additional sensitivity to the serum-based MALDI-TOF MS-based assays. The sensitivity of FLC-MS for the detection of low-level residual monoclonal FLC was also enhanced by on-bead de-glycosylation in patients with light chain N-linked glycosylation. The first clinical study included in this thesis explored the sensitivity and prognostic utility of MALDI-TOF MS in patients being treated with carfilzomib, cyclophosphamide, lenalidomide, and dexamethasone (KCRD) in the Myeloma XI trial. In this work MALDI-TOF MS provided greater sensitivity for the detection of residual monoclonal protein compared to electrophoretic techniques and MALDI-TOF MS negativity was associated improved progression free survival (PFS). In addition, FLC-MS negativity in patients with no residual monoclonal protein detection by immunofixation electrophoresis at the end of induction, day+100 post autologous stem cell transplant (ASCT) and six months post maintenance randomisation was associated with reduced PFS. The second clinical study evaluated the utility of MALDI-TOF MS in patients with non measurable myeloma. This study showed that 91% of patients classified as having non-secretory myeloma using standard techniques have detectable monoclonal protein in the serum using MALDI-TOF MS. MALDI-TOF MS also provided greater sensitivity for monitoring patients with oligo-secretory myeloma. Further studies should therefore be undertaken to establish criteria for measurable disease using MS. The third clinical study included in this thesis evaluated the utility of a FLC specific MALDI-TOF MS assay in patients undergoing treatment for AL amyloidosis in the ALchemy study. This is the first study to evaluate the prognostic utility of a FLC specific MS-based assay in patients with AL amyloidosis and found that achieving FLC-MS negativity at six and 12 months post treatment initiation was associated with improved overall survival. There was also an improved rate of renal responses amongst patients who achieved FLC-MS negativity at 12 months. The final clinical study included in this thesis is the first study to evaluate the prognostic significance of light chain N-linked glycosylation in patients undergoing treatment for PCD. This study included patients treated with KCRD and ASCT for multiple myeloma and bortezomib-based treatment for AL amyloidosis. In contrast to the higher risk associated with light chain N-linked glycosylation in patients with monoclonal gammopathy of undetermined significance previously described by Dispenzieri et al this work found that light chain glycosylation was not associated with inferior responses to treatment or reduced survival