Heavy and Light Chain Monitoring in High Risk Smoldering Multiple Myeloma Patients Included in the GEM-CESAR Trial: Comparison with Conventional and Minimal Residual Disease IMWG Response Assessment

Introduction: The GEM-CESAR trial is a potentially curative strategy for high-risk smoldering multiple myeloma (HRsMM) patients (pts) in which the primary endpoint is the achievement of bone marrow minimal residual disease (MRD) negativity. However, other methods of disease evaluation in serum such as heavy+light chain (HLC) assessment, with a potential complementary value to the IMWG response criteria, have also been tested.

Aim: To evaluate the performance of HLC assay in HRsMM pts at diagnosis and after consolidation, comparing the results with standard serological methods and Next Generation Flow (NGF) for the assessment of bone marrow MRD.

Patients and Methods: Ninety HRsMM pts included in the GEM-CESAR trial received six 4-weeks cycles of carfilzomib, lenalidomide and dexamethasone followed by high dose melphalan and 2 further cycles of consolidation with the same regimen. All pts received maintenance treatment with lenalidomide for up to 2 years. SPEP and IFE were performed using standard procedures. Serum IgGk, IgGl, IgAk and IgAl HLC concentrations were measured using Hevylite (The Binding Site Group Ltd, Birmingham, UK) on a SPA PLUS turbidimeter. HLC concentrations and ratios were considered abnormal if they were outside the 95% reference ranges provided by the manufacturer. MRD was analyzed by flow cytometry following EuroFlow recommendations (sensitivity, 2x10^-6). Standard response assignment was carried out as per the IMWG guidelines. Hevylite responses were assigned and HLC-pair suppression was defined as in Michalet et al (Leukemia 2018).

Results:

Out of 90 HRsMM pts, 75 had monoclonal intact immunoglobulin and samples available at diagnosis (50 IgG and 25 IgA). HLC ratio was abnormal in 98% of IgG pts and in 100% of IgA pts. Response assessment by Hevylite and standard IMWG criteria were available in 62 pts post-consolidation (Table 1). A good agreement was found between the two methods (kappa quadratic weighting = 0,6327 (0,4016 - 0,8638)). Among 46 pts with assigned CR as per the IMWG response criteria, there were 3 and 8 pts in PR and VGPR according to the Hevylite method, respectively. In 62 cases, paired Hevylite and MRD assessment data were available. Concordant results were found in 72.5% of cases (45/62; HLC+/NGF+ in 15 and HLC-/NGF- in 30 cases) while in the remaining 27.4% of cases results were discordant (17/62; HLC-/NGF+ in 6 and HLC+/NGF- in 11 cases). Post-consolidation, 24, 25.8 and 42.3% of the 62 samples were positive by SPEP, NGF and Hevylite, respectively. HLC-pair suppression was identified in 13/62 pts; 10 had severe HLC-pair suppression at the end of consolidation. After a median follow-up of 32 months (8-128), 93% of pts remain alive and progression-free. Three patients that have already progressed had their responses assessed post-consolidation. The first pt was assigned VGPR by the standard IMWG criteria and PR by Hevylite and was MRD positive by NGF; the second pt was assigned CR by IMWG criteria and Hevylite but had severe HLC-pair immunosuppression and was MRD positive by NGF; the third pt was in CR by IMWG and HLC criteria and was MRD positive by MFC.

Conclusions: Moderate agreement was found between response assessment by Hevylite and the standard IMWG methods as well as between Hevylite and MRD assessment by NGF. Most discordances were a result of Hevylite detecting disease in samples negative by the standard methods, but longer follow-up is needed to ascertain its clinical value. HLC assessment could have anticipated the progression noted in 2 (out of 3) patients.

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