Testing Mayo Clinic’s new 20/20/20 risk stratification model in another cohort of smoldering myeloma patients: A retrospective study.

e20005 Background: Smoldering multiple myeloma (SMM) is an asymptomatic plasma cell disorder associated with a high risk of transformation to symptomatic multiple myeloma (MM). SMM risk of progression to MM is highly heterogeneous and several models have been suggested to predict this risk, but none have yet been adopted internationally. Lakshman et al. recently proposed a risk stratification model based on three markers: bone marrow plasma cell (BMPC) percentage > 20%, free light chain ratio (FLCr) > 20 and serum M protein > 20 g/L. In this “20/20/20” model, patients with 0, 1 or ≥ 2 risk factors are respectively considered at low, intermediate and high-risk of progression. The goal of our study was to test this risk model in our population and to determine if similar results could be obtained in another cohort of SMM patients. Methods: We conducted a retrospective, single center study with 89 patients diagnosed with SMM between January 2008 and December 2019. Patients were identified by query of the electronic medical records and the 2014 International Myeloma Working Group (IMWG) diagnostic criteria for SMM were used to determine eligibility. The main endpoint was progression to symptomatic multiple myeloma or amyloidosis. Results: All three markers proposed by Lakshman et al. were associated with an increased risk of progression: BMPC percentage ≥ 20% (hazard ratio [HR]: 4.28 [95% C.I., 1.90 – 9.61]; p < 0.001), serum M protein ≥ 20g/L (HR: 4.20 [95% C.I., 1.90 – 15.53]; p = 0.032) and FLCr ≥ 20 (HR: 3.25 [95% C.I., 1.09 – 9.71]; p = 0.035). Immunoparesis (HR: 2.61 [95% C.I., 1.07 – 6.41]; p = 0.036) was also an independent risk factor in our population. The estimated median time to progression (TTP) was not reached for the low and intermediate risk groups and was 29.1 months (95% C.I., 3.9 – 54.4) in the high-risk group (p = 0.006). The estimated mean TTP for the low-risk group, the intermediate-risk group and the high-risk group were respectively 78.4 months (95% C.I., 68.3 – 88.5), 48.3 months (95% C.I., 31.9 – 64.8) and 35.2 months (95% C.I., 19.1 – 51.2). Sex, IgA isotype, positive Bence-Jones, abnormal β2-microglobulin and MGUS prior to SMM did not result in an increased risk of progression. The estimated proportion of progression-free patients at 1, 2 and 5 years were 96.8%, 93.4% and 77.5% for the low-risk group, 80.0%, 80.0% and 62.2% for the intermediate risk group and 70.0%, 58.3% and 29.2% for the high-risk group. Conclusions: When Mayo Clinic’s new 20/20/20 risk model was applied to our population, it adequately predicted the risk of progression to symptomatic disease at 2 years. As it relies on readily available biological parameters, this model is easy to use and can be applied in most clinical settings. We believe this model could be used to further study therapeutic approaches in higher risk SMM.

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