Clinical characteristics and outcomes in risk-stratified patients with smoldering multiple myeloma: data from the Czech Republic Registry of Monoclonal Gammopathies.

Smoldering multiple myeloma (SMM) is an asymptomatic precursor to active multiple myeloma (MM). The aim of this study was to report clinical characteristics and outcomes of patients with SMM stratified based on their risk of progression to MM using the Mayo 20/2/20 criteria. Data were leveraged from the Czech Myeloma Group Registry of Monoclonal Gammopathies (RMG). Key outcomes included progression-free survival from SMM diagnosis to active MM diagnosis or death (PFS), progression-free survival from SMM diagnosis to progression on first line (1 L) MM treatment or death (PFS2), and overall survival (OS). Of 498 patients, 174 (34.9%) were classified as high risk and 324 (65.1%) as non-high risk. Median follow-up was approximately 65 months. During follow-up, more patients in the high-risk vs non-high-risk group received 1 L MM treatment (76.4% vs 46.6%, p < 0.001). PFS, PFS2, and OS were significantly shorter in high-risk vs non-high-risk patients (13.2 vs 56.6 months, p < 0.001; 49.9 vs 84.9 months, p < 0.001; 93.2 vs 131.1 months, p = 0.012, respectively). The results of this study add to the growing body of evidence that patients with high-risk vs non-high-risk SMM have significantly worse outcomes, including OS.